If SD13 is going to continue to lie and wreak havoc on your home, you can prove her right and she won't be welcome. Your DH can exercise his visitation elsewhere if she's going to act that way. Or even better, she can just stay with DH and BM's messed up extended families and stop visits all together. Let the toxic enmeshment occur without you all. 

I would have hung up on bio moms dad. But then again I wouldn't have probably answered to begin with. It seems like alienation from them 

She didn't bring this baby into the world, it's not her job to watch her. My cousin won't let anyone call her brother her half-brother - he's her brother. But not everyone has as big a heart as she does. It's not a hill to die on, just stop making her responsible, she's probably jealous that baby is with Dad 100%. 

When I finally had it with SD crap after 12 years (she was 17-1/2) I firmly told DH that he could still exercise his visitation rights, it just couldn't be in my home. He could do it at his parents, his sisters, a restaurant, I didn't care - but my home is my sanctuary and I'm not going to be treated like dirt here. And a lot of it was him - how he non-parented and then sided with her. Nope, done. He just stopped exercising his visitation altogether. Interesting. Didn't have a woman to do the parenting (relatives would have expected him to be the parent, not them), so he stopped doing visitation at all. Wish I'd laid down that law years before. It was so toxic here. 

Lesson learnt and never again answer any phone calls/text messages from ex in-laws.

If they keep calling/texting, just simply text back that you don't want them to contact you in any form or you'd make harassing report with the police. 
Please don't explain yourselves to anyone. Your stepdaughter will have to suck it up having chores while in your house. Your husband needs to grow balls. 
You actually have a husband problem, but you probably already know that. 

That is the exact message that DH needs to give BM's polluted gene pool sire.

Reminding Grampa Turd Genes Daddy that his daughter is a POS and he gets no say in how DH's children are raised.

Now for DH, if he wants to maintain the high ground in all of this, he needs to pay his CS in full and on time every month.  PERIOD DOT!  Not a penny more, but never a penny less, and never late.  If DH is paying BM directly, he needs to engage the Child Support Enforcement office and have his CS paid directly to that office and then they forward the CS to BM. That way, WombGrandPa can be told that CS is paid monthly to the CSE office and BM call them for her money as WombGrandPa is not a party to the case and gets no opinion.

Even better would be if DH requested direct payroll withholding for his  CS obligation. That ends any discussion of CS payment. From BM or her over stepping toxic daddy.

All IMHO of course.

my advice? 

1. get the cs balance to 0, keep it at 0. 

2. block exes-Dad, block exes-mom, block her sister, her brother, her third cousin twice removed on her dad's side. blockity block block their numbers. 

3. all visitation is now taken elsewhere. SD's lies are escalating and now that it's affecting your home... she cannot be there. 

4. stop replying, stop texting, stop answering to SD's maternal family. unless it is important, let it go to text, voice mail, email. especially from SD's mom or SD herself. 

You are living my biggest fear- all it takes is one lie to the wrong person and CPS is breaking up your family. She lies to her family they could easily call as it is. Do NOT let her into your house.
 

He can have visitation elsewhere and I would have DH tell her plainly, "due the lies you have spread about this household you are no longer allowed to be here as it is not safe. That will not change unless you apologize. Short of that the ball is in your court to reach out to me when you'd like to connect outside of the home. I will not spend my energy chasing someone who does not want to be caught." 
 

fucking done

Wow! SD is quite a brat. Her grandpa is too. I would cut them both off - ban them from the house. After all, in her family's eyes you are already the devil, so why not cut that little b**** out of your life until she can fly right? 

I feel bad for her father, but unless he has a come to Jesus meeting about her terrible behavior, then it will continue. He has to have steep consequences for her lies. Maybe if he enforces the rules better, she will not even want to come to his house anymore. She will want to live with BM, who coddles her. That is what happened with my SD. Now she is 21 and still banned from our home. Until she grows up a little, she can just f*** off, as she has told me to do many times before. LOL.

I agree with the blocking of the Exes father.. it's not his place to call your DH on the carpet.... 

But.. it sounds like things were not necessarily outright lies?? perhaps some exagerations?  like the CS.. that maybe is late or a bit short.. but not in any material way.. but BM likely whines to her parents so they will send money her way.. 

And.. SD.. IS asked to watch her siblings.. and that should probably stop.. I don't think a kid with her lack of connection with your smaller kids/baby should be in charge of them.. in any way really.  And.. your home does seem like it isn't very welcoming to her.. but you have other kids.. the world doesn't always revolve around one person.. but with all the littles at your place.. it's probably not a welcoming environment for a 13 yo girl.. and her dad seems to be elsewhere even when she does decide to come.  Dont' get me wrong.. you have outside forces pulling her away.. but the things she said do have a reflection of her feeling of how your home is set up with regards to her.. and the expectation that she "pitch in".. she is there so little .. she probably isn't comfortable or liking that.. and he is her father.. so it' his job to tell her what to do.. but again.. she may have magnified the role for sympathy.. or your DHS EX inlaws are twisting it.. or BM is twisting what SD said?.. it may not be outright lies by SD at all.

and she is 13.. banning a kid for what she has said.. even if she DID say it.. you can't ban his child because you think she is a brat.. it's his child for gosh sakes.