A lot of us here are sadly well acquainted with toxic BMs.   Like yours, mine told the SDs lots of lies about me, and it took them about 15 yrs to realise it.   At least your SD17 is OK with you - and hopefully she will set an example for her younger sister.  

She tells them that I am a bad person, that they should not spend time with me or my daughter while they are here, that I am trying to be their mother and replace her (!) and even gone so far as to say that I was having an affair with their dad for ten years and I "broke up their family" (!). Whenever the SDs are with us she will call their cell phones incessantly until they answer and demand to know exactly what they are doing and with whom. I never comment on any of these issues in front of my SDs, have never said a bad word about their mom

This was BM to a T, when DH and I started getting serious in our relationship and had just signed a lease on an apartment together. 

Mind you, SD was only 6-years-old when she’d say these things to SD in hopes that it would get back to me via SD and it did.

I just smiled and nodded, while DH became furiously livid with BM’s antics. 

All I can constructively add is that your husband needs to be the one to address this. In-person with his daughter - and perhaps get her into therapy if she already isn’t. Secondly, he needs to address BM in a manner that there will be a paper trail. That’s what my husband’s attorney advised him to do. Email works best. He needs to remove all emotion from his communication when he approaches BM about this. He needs to communicate with BM in a manner in which he will obviously appear as the bigger, better person and parent if this were to cross an attorney’s or judge’s desk. Firmness and consistency is key. 

While it did squash BM’s crazy there for awhile, it hasn’t totally gone away, and that was over 8 years ago. 

Welcome, I hope that you find this to be a good place to vent, contribute and to pick up some useful perspective from others who are living the blended farmily dream.

The blaring issue in your post is the absence of your husband in dealing with all of this. He and he alone can fix this. Both getting his X under control and getting his 13yo the help she needs and dragging her into participating in his family.

So, where is he?  And why is he putting all of this on you instead of manning up and dealing with his problems himself?

to what you are experiencing and boy its not fun.

I found that it was a lose lose situation, I lost if i ignored her or played nice and accomodating, I lost if i retaliated. there is no middle ground because shell just use the SD13 as a weapon and torture her.

As RAGS said above, emphasis has to be given back to your SO to fix/stop this cr@p with the X. There has to be a zero tolerance policy to her abuse. Atleast his girls sound like nice kids, and even if the relationship between you and SD13 isnt super close I honestly think in time it will be. Youll be the stable one, she will seek out your time as opposed to her unstable mothers.

Just keep loving them, supporting them and Ignore the wicked X, she needs none of your time or energy. Let her do what she needs to do to validate herself.

Those girls will grow up knowing the difference between emotional abuse and stability, Just keep doing you. She'll meet someone eventually and shut up.

I feel for you, My husband has a crazy abusive ex partner too. It's been five years and she is still the same. I keep hoping she will meet someone and will finally move on.

Best thing I can suggest is learning ways to minimise the impact.

we do gray rock method with her. Only respond when we need to and keep it business like. No emotion, nothing personal. Much better when you don't engage with the crazy.

The hardest is the things she says to my step daughter. After five years I have accepted that some things are just out of your control. Take the high road , don't respond or talk bad about her. Be kind and good role model for the kids. The kids will work her out themeselves. 

Find close friends and family you can vent too xx

The high road includes keeping Skids fully abreast of the absolute and total facts regarding the toxic, manipulative and shallow end of their gene pool, if they are unfortunate to have a shallow and polluted end of their gene pool.

This gives them the tools they need to protect themselves from a toxic parent and/or extended family as they grow up and through their adulthood.  Toxic assholes need to be eternally tormented with the facts by the quality end of a kids gene pool and by the kids as they grow up.

My own SS (adopted at his request at 22yo though I became his dad when his mom and I started dating when he was 15mos old and for sure when his mom married me the week before he was 15mos old.) knew at a very young age that his SpermClan was neglectful, abusive, toxic, manipulative and generally a collective pile of shit.  We did anything necessary to protect him from their crap and to arm him to be able to protect himself from their crap over the years and... remain compliant with the visitation element of the CO we lived under for 16+ years.

At 27yo he is fully  capable of dealing with their crap and he has repeatedly bared their lying toxic asses and shredded them brutally when they step out of line in their interaction with him.  Crap like regularly attempting to guilt him into providing money for the support of his three younger also out of wedlock SpermIdiot spawned half sibs by two other baby mamas, etc..... 

He will tolerate no crap from any of them.

They said all kinds of crap about how unfair it was for SS to have quality clothes, opportunities his younger SpermIdiot spawned half sibs did not have, that the CS they were forced to pay ($110/mo for a year, $133/mo for 9 years, $385/mo for 6 years) was taking food out of the mouths of his three younger polluted end of his gene pool half sibs.

They taught him to recognize toxic manipulative bullshit and they taught him how to treat them.

His mom and I have always had his back and always will.

He is kicking butt, and alone is far more successful than his entire SpermClan gene pool combined and lives his best life and and perpetrates his own awesome revenge on they by living that life every day.

People who create stench and are nasty POS assholes to innocent kids need to have their noses rubbed in their stinky spot in life's carpet by those taking their revenge. The kids need the facts to protect themselves and to exact their revenge by living well.

IMHO of course.

My husband's ex has also had a negative attitude about me from the beginning.  It intensified once we got married.  The funny thing is SHE wanted a divorce, not him.  It's been 6 years since they divorced now, and she is still single, no boyfriend.  She is so rude to me, and basically won't even speak to me when I see her.  She acts like I was his mistress or something...I didn't even meet him until they'd been divorced 2 years!  She tells the kids negative things about me.  This is my 3rd marriage, and she TOLD them that I would never stick around.  Told my husband the same thing.  She has some nerve because she doesn't know any circumstances surrounding my other marriages and I had very, very good reasons for divorcing.  She told them I am a bad person, and I know that because my stepson actually said "you're a bad person" to me one day.  That's not something a teenage boy would just say for no reason.  She also tells them that their dad is rich, but only wants to spend his money on me and my daughter.  Which is so dumb because my daughter's school is free and they both go to expensive private schools!!

I do have some encouraging words for you...It CAN get better.  Their attitudes towards me have greatly improved over the last few months.  It's not perfect, but much much better.  The three ways we fixed it

1. My husband told them several times that I am NOT going anywhere and that he loves me, I make him happy.  That this is their family whether they like it or not and they need to be respectful.  He told them that they need to stop listening to their mom and treating me as if I am somehow to blame for their family not being intact.  That I had nothing to do with the divorce and haven't done anything wrong.

2. I had a family meeting with my husband and two stepchildren.  I explained our budget, put it in a pie chart, and proved to them that the idea they have about us "being rich and not spending money on them" was absurd and to put it out of their minds.  I also said that they are always uptight when they are home with us and need to loosen up a bit.  I said that "I really hoped they weren't going home and thinking or saying negative things about us"  because negative thought and negative talk breeds negative feelings and causes everyone to feel sad.  I told them that we are not the enemy, and this is not a war.  I told them that I know they have a good mom and that she loves them and takes good care of them.  (I've never said anything negative about her to them)  That I love them, their dad loves them... and it's that simple.

3. I started to let my guard down just a little (It's really not easy because they make me feel extremely uncomfortable sometimes) and started to talk to them a little more and spend more time with them.

I don't know if any of this will work for you, and trust me it's not even close to perfect.  (It's so bad that I saw my SS and his mom at the store, and he motioned for me to leave them alone.  He was obviously nervous about me talking to his mom.  I can't even say hello to my stepkids in the store.  How pathetic!)  It's just gotten a little better than it used to be.