You are going to have to take control of this situation since your DH won't. YOU have a birthday party for your kids and your SD is NOT allowed to attend. If you are comfortable with it, your DH can take the birthday child to dinner and his crazy daughter can celebrate the birthday then. This would not be a request to my DH..it would be a demand. Next, talk with your kids, being age appropriate. You can say something like, SD cannot make your party so dad and her will take you out later for dinner, or a multitude of other excuses.

As for your DHs birthday, two seperate celebrations. You and your kids do something with him and his daugther(s) can plan something. I'd strongly suggest looking at Christmas the same way. I cannot imagine being in the same room with someone who spoke to me that way. While I'll offer grace, we would part ways. Wish them the best but we stay apart. In fact, that's how I now operate with DHs bunch. (We had a failed attempt at reunification where I saw absolutely zero changed behavior. It was a no-go for me).

Of utmost necessity is to block this woman on all communication areas. Phone, text, social media, email, etc. You cannot control what she does but you can control her access to you. 

What your SD did demands some serious consequences. Your DH should seriously consider seeing his toxic daughter away from the marital home. 

I'm so sorry for your situation. Take care of you and those kids. You don't want that nasty SD influencing or impacting your children. Remember, your daughter, in her breakdown, also heard what your SD was saying about you. THAT did not help your daughter's situation....probably made it worse. Protect your child from this woman.

I'd definitely not allow her in my home or around me ever again.  I'd also be concerned about her being around my children.  She called you the c word and screamed at you in front of your daughter.  What would stop her from poisoning your kids against you when you're not around? She already poisoned your other SD's against you.  She sounds like the type to poison your kids against you too, and she'd be proud of herself for it.  

I also worry in this case that the SD'S will eventually turn on their younger sisters.  This is partly why I don't allow my SS and his wife to have contact with my bios.  Why would I allow someone contact with my kids who hates me, their mother?  Either they'll turn on my kids or turn my kids against me.  Or both. 

If it were I, I'd make it clear that that daughter is not allowed on your property, not allowed access to you in any way, is blocked from all of your social media, etc. If your husband wishes to see her, he may do so alone and in a different location. And I wold make it very clear that these are permanent rules. If she shows up at your door you will be calling law enforcement and having her removed. That with the issues you younger child is having this SD is not allowed unsupervised contact w/ her. That all contact w/ your daughter is through Dad. No direct contact via cell phone, e-mail or social media of any form. You will be blocking SD fron all of those items. That the stress of this SD is detrimental to your child's mental health and you will not allow it any longer. That should she try to bypass your rules, you will seek a no-contact order through the courts. .

Make it clear that your minor child comes first now, SD is an adult and will no longer be treated w/ kindness by you. She placed your child in harm's way w/ her attack on you and that is the final straw. 

I would consider this a "last straw".  I think it's time for an ultimatum with your husband on this.

In no uncertain terms.. you will not SD30 in your home.  She is not welcome at any parties that you host.. and you will not attend any parties hosted by others where she will be in attendance.

Give him the 30,000 feet explanation that is.

I have bent over backwards to be nice and civil to all your daughters.. for some reason that NO ONE can explain to me, your oldest daughter hates me.. and uses every opportunity to attack me and turn people against me.  My only sin  that I can see was that I tried to raise them as my own when their own mother would not be involved.  After this most recent outburst in front of my mentally fragile 12 year old daughter, I am done being the nice guy who just accepts her abuse. I'm done.. I don't want to see her.. have her around my children.. that's it.  You are free to have a relationship with her.. OUTSIDE of our home. that is it.  At this point.. I am throwing in the rope and any hope that she would stop seeing me as some villian. 

This gets your daughters off the hook for the wedding.

Why was she even at your house on a Monday morning? Was your DH so distraught that he called his 30-year-old daughter to his house to help? I agree. No more SD at your house. You guys have to manage your 12-year-old without the help of the SDs. If your hand-wringing DH can't manage that, restraining order. 

Dup

I don't understand how your SD's can possibly be helping your 12-year-old with her issues when they are shouting at you and calling you the c-word. Attacking the mom of a struggling teenager sounds like the last thing she needs. That must be VERY confusing for your daughter.

I'd be in full Mama Bear mode. Remember you are a role model for your daughter and she is watching how you handle their abuse. Remaining calm in the moment is admirable -- but now it's time for action. Abuse is never acceptable, and by exposing her to their lies and accusations and anger, your daughter is being abused too.

I tried with her, but it just never "took".

Shes not going to be allowed to come over. Husband can have his relationship with her somewhere else.

Id get a restraining order for yourself as well as your daughter. Sd and Husband are the least of your worries at this moment.

Take some time off with your kiddo. If you can afford it.

Any chance your DD's health issues are related to manipulation tactics by wacko SD?

I'd be curious what DD's therapist would say about this.

This is all on your "D"H for letting SDs behave this way for so long. I'd be extremely resentful of him for allowing this. 

It's troubling to me that your DH did not put a stop to that behavior. If he wants to continue to have a relationship with this hateful daughter, he needs to do so on his own time in his own space that is not your space. I would explain to my daughter that I thought SD behaved very inappropriately and I did not feel comfortable with her being around my children for their own safety. I would probably be at the point where I would tell my DH that maybe he needed to move out for a while, if he thought that his daughter's behavior was okay. It seems like she crossed many lines...and she can't uncross them. 

Your daughter are going through this. But here's an opportunity for you to set an example for your daughter about boundaries and what we tolerate from other people.  This outburst at such an inappropriate time is not the type of behavior that gets excused or swept under the rug or otherwise dismissed.  She raged and cursed at you in your home, in the presence of your child during a mental health crisis. Never again would she have such an opportunity!

On one hand, I would love for you to be able to rebutt her claims and tell her how you stepped in when BM bounced,  but it's probably not even worth it because people like that don't hear truth in anything. 

Make it clear to DH that this episode was the last. You're not a punching bag for her frustrations and you're no longer including her in your life. 

I don't care what kind of relationship SD has had with BDs, as of now contact is over because a grown ass woman raged while you were attending to your child and weren't in a position to deal with her and her issues. To hell with her.

If extended family ask about the situation,  tell them the truth. Hopefully DH has enough spine to do the same. 

A restraining order isn't a bad idea at all.

Exclude her from every event,  holiday,  birthday,  celebration or gathering because she's poison.  

I strongly suspect DH wouldn't tolerate being spoken to or treated that way by someone else,  regardless of whether it was your child or a stranger,  so why should you?

Be the example of setting boundaries so your daughters know it's ok to protect yourself from toxic people.  It may save them more heartache in the long run,  especially if SD should ever turn against them. You're not the bad guy, do don't let anyone make you feel that you are.

I have kept my youngest away from 3 of the skids.  They turned to violence as teens and decided then to keep them away from YBD14.  She knows they exist but has no memory of them.  She was a baby when it all went down.  OP, you should not doubt your role as their mother and keep toxic people away from your bios.  It's too bad they are half siblings but the toxicity trumps that.  Pulling them from the wedding might be sad for them but the skids NEED logical consequences for this behaviors.  If DH can't do it then you do it.  Be momma bear wearing bitch boots.  Show your girls how a real women handles business.  And more importantly , explain exactly WHY.  They need to know.  

PERIOD. Or in any other human interfaces for that matter.

The reason for the ill behavior, is not relevant IMHO.

They behave, or they are shunned.

Direct consequence for behavioral choices drives different choices.

IMHO of course.

Yes, my usual black and white perspective. When it comes to behavior, there should be no grey. It is either reasonable and acceptable, or it is not.

I have struggled with medicated on the spectrum and medicated anxiety suffering key team members at work for more than a year. I now understand that PTSD is a thing because I have experienced it for myself.  Not knowing from minute to minute what I was going to get from the medicated leaders on my team.  One minute absolute brilliance and professionalism, the next dominating aggression, emotional callapse, etc....  As they have left my team, the entire team performance has improved. My morning commute is no longer an anxiety building journey.

I still have stress reactions to both of those individuals when they inject into my organization from their new roles in other facilities.  

I waffle on supporting them, mentoring, and developing them. They are both technically brilliant though they have almost no discernable emotional intelligence.  I am in an odd position of recognizing and presenting them awards for technical performance, while reprimanding them formally for behavioral and people treatment issues.  I have landed on the position that however great they are at their job, they are a detriment to my business and my team... so..... I now document everything formally, tolerate zero deviations from standards of behavior, and .... they are now on very thin ice due to me going to a the rules are the rules perspective.

My entire team has commented on how much better our team performs and how much better our relationships with other organizations and our customer are with those two gone.

Both have attempted to return to my organization.  Not no but hell no.  Fortunately, my customer shut that down in a heart beat.  I said no, my upstream leaders tried to end run to my customer, the customer put a stop to that mess.  My boss called and asked if I had spoken with my customer about the possibility of the return of one or both of the medicated individuals. No, I  had not.  My customer and I have a very good relationship and regular communication.  We have both suffered from the behavioral volatility of the two perpetrators.

My upstream leaders are freaking out that the seat that they both had filled sequentially is vacant.  I would rather have it vacant than have either one of them back in it.  My goal is to prevent a repeat of past situations.  I am having direct converstions with the managers of applicants for the vacancy in an effort to prevent a third in a row unstable #2.

My own quality of life as well as my own mental/emotional health gives me no choice.

Personally, I like both of them very much.