The boundaries he needs to set depend on her behaviors. Without more details on what your marraige needs protection from, it's hard to give advice.

So, for example, the minute your SD starts becoming disrespectful to you or her father, the conversation/gathering/what-have-you needs to end. Say, "We will not be disrespected," and hang up the phone or leave (or she is told to leave).

You become intolerant to disrespect and manipulation. You shut down the conversation and do not engage in arguing with her. Repeat as needed, but generally speaking, toxic people don't magically cure themselves at the age of 38. 

My toxic brother is approaching 41 and the only boundary I have found to keep his crazy from my life has been to completely cut him out of it.

I also agree that since these are adults who aren't living in your home.. what exactly is happening that you need to have stopped?

Are they coming to your home unnanounced and coming in uninvited? 

Are they excluding you from invitations or when present at events are they rude to you?

Do they complain to your husband about you?

Again, with adults out of the home, there should be almost zero need for you to interact with them at all.  And as far as your husband.. when they say the first thing bad about you.. when he does speak with them.. he clearly tells them that he will not listen to their poor-mouthing and that when they are ready to apologize for speaking badly of his wife.. they can speak again.

If they persist in being generally nasty.. they don't get the opportunity to BE nasty.. they don't get invitations to holidays.. they don't get calls.. they don't get their father's (or your) support..They basically become persona non grata in your home

We sort of went through a similiar timeline and issue.

Because you're both reading this, I don't want to let him off the hook for setting boundaries with his kids. But I found my husband is not capabale of defending me nor setting boundaries with SD that look like boundaries. It all had to be cloaked in some other motive for my husband to set a boundary, but at least it achieved the same result.

So, for example, rather than asking SD not to call at 7 a.m. unless it's an emergency, he just turns off his phone until a decent hour. When she asks him why he didn't answer, he might say, "I was up late last night working" or "I forgot it was shut off." It works - no more calls at the crack of dawn. But it would have been nice if he had been comfortable telling her the truth. It would have been good for her to hear a boundary exists and it would have set a new tone for things -- like, hey, I'm married now, so please be considerate of someone else in the house. (She knows no boundaries -- she called on our honeymoon to talk for hours about her mom!) These little reminders to her might have made her more considerate of me in many aspects. But I had to take what I could get: Just getting him to ignore a call from her took months of therapy with all his daddy guilt.

So I guess where we landed was I made a complaint to him, he'd sometimes figure out a way to address it without upsetting SD and sometimes it worked. My husband has never felt comfortable with his power to change the dynamic among the three of us. As a result, I disengaged a few years ago. I think he hates having his life split in two, but he was the one who held all the power and he didn't want to use it.

I urge honesty in dealing with skids rather than this "secret" way my husband addressed complaints about SD. It wasn't fair to SD to never treat her like the 30-something she is -- I would have loved it if he had said, "Honey, I'm on my honeymoon. Anything with your mom can wait until I'm home. Love you, bye." He never would call her on HER honeymoon to complain about anything! Why not just give her a boundary so she sees what she's doing rather than hoping she figures it out on her own???

You're really trying to reset the relationship between your husband and the problem skid. If he isn't honest about his boundaries, your SD will never learn and every issue will BE an issue because the kid doesn't know a line has been drawn.

In the end, it was easier to disengage than deal with an aggressive, assertive SD and a weak, guilty father. But I hope it goes better for you.

I am in a very similar situation.  I will be watching and reading the responses you get.  I have two SD's both, now out of the house (thank goodness)  They are 28 lives in same town as DH and I and the other is 27 (recently moved to TX to get closer to her mother that of which she can't stand.  She had a little one and left the father).  Even though they are not longer in our house - it is their house apparently.  When they come over they go through what I compare to "marking the house".  Everything is up for grabs.  In addition to this, they totally ignore me and the boys.  That is fine but up until I decided to disengage it was heartbreaking in the terms of the effort I tried putting into developing a relationship.  They are just plain bitter.  The biggest eye opener has been the amount of lies they tell - about things that they don't even have to lie about.  I don't  get it.  We are where we are because of the "guilty father syndrome" and my DH did not implement boundaries at all -even before we met (married 9 years, dated 2 years).  Ugh - It gets so old!!!  

First I want to say my hat is tipped off to you because I don't know how you lasted 15 years in such a toxic dynamic, especially with a man that didn't set boundaries, didn't support you, and have your back. Now back to your question at hand like a poster commented above your H has to be open, honest, and consistent about his boundaries. This is years of dysfunctional behavior so its not going to work over night. What ever he says if not followed through needs to have consequences behind it which will cause conflict. He has to be prepared for this and handle it accordingly. If he doesn't your marriage will remain in disrepair and you can expect to live another 15 years in this f@ckery.

So if your H is reading this and I hope he is, he has to "man up" and teach his daughters to respect you and your marriage.

And to your DH, your DD's are going to use emotional blackmail as a manipulation tool to get you to 'fall back in line' (dad you will never see or hear from me again, you will never see the grandkids, we will not see you unless you leave your DW at home,  etc). Do not, under any circumstance, give in to their manipulation and start back allowing them to run over you and your DW and do NOT chase them. Stand your ground and it may take 1 year or 2 of them not coming around or calling to 'punish' daddy but he has to shut this behavior down and he is dealing with a master manipulator (30 plus years of allowing her to run the show). 

Support each other and keep busy doing things that you two like. Your SD's are going to try several different tactics and you all need to know ahead of time what it is and stand as a United front. Good luck and big hugs.

Your story really warms my heart and demonstrates that marriages can be saved if the parties are committed to working together towards healthy goals. And kudos to your husband for stepping up, owning his mistakes, and resolving to do better.

I think when one member of a dysfunctional dynamic decides to get healthy, it's unrealistic to expect support or cooperation from the other members. So the focus shouldn't be on whether or not the SDs get with the new program. You can't control that outcome, and they may never change. But if the two of you focus on doing the right things for your marriage - you avoiding hurtful toxicity and your H protecting you and being consistent with boundaries - and let go of any expectations, you'll have a better result. These adult children are who they are, and in my perfect scenario your H would speak to them individually, apologize for his parening mistakes, and let them know what the rules are going forward.

There will be pushback, and bad behavior will likey ramp up so gird your loins. Hold tight, and love each other hard. I went through something similar, and while the outcome hasn't been what we hoped for, our marriage is much stronger and loving. 

I don't have to deal with adult skids yet, thankfully. However, I don't see why this can't be handled in "Family Meeting- our house 5 pm. Not coming is not an option." Sit everyone down at the diningroom table and talk it out. If the adults storm out of the room, refuse to be cordial and polite to you, or don't show up- then fine. They made their choices. Actions have consequences. It is time they figure that out and Christmas time when their hands are out looking for presents is a great time to show that. 

This is your husband and daughters drama, they are reliving and replaying the first family dynamics over and over.  DH was the white knight trying to save his daughters from their mother then DH tried to replace his ex with a new "mom" (you) that he could control but it backfired for all involved.  Now you want him to save you from his daughters. Step out of the arena, give them back their relationship and disengage.  

The only winner is this situation is the ex-wife who has been sitting back, eating popcorn and laughing all these years watching you guys persecute each other in her name.  

It's hard to change the dynamic after all those years. I am in the same situation and had a conversation about it with DH just last night. In my case, SD acts like the parent telling DH what to do and DH acts like the child doing it to please her. He admits to being scared that she won't love him so he does what she wants, and I sit on the sidelines. Apparently he's not afraid that I will stop loving him. And I've let this go on for way too long.

Your SDs are adults. I suggest approaching it with honesty and not game playing. Set new boundaries for whatever the issues are and TELL them what the boundary is and what the consequences will be if they cross it. THEN FOLLOW THROUGH. If a boundary is crossed but nothing is done about it, that is a wide open invitation to cross that boundary again.