Need advice on what to do with my stepdaughter and daughter

A little background on my stepdaughter. Shes 15 and has seen her parents fight her whole life so I’m not 100% blaming the mother because my husband could definitely deal with the mother a whole lot better. Here are some of the things I have witnessed the mother do:

-tell the daughter that my husband is kidnapping her while the daughter is crying

-told the daughter that my husband physically abused her while they were in a relationship 9 years ago and went to jail for it

- have attempted to drive us off the road

- have told the daughter to walk outside at 2am while my husband and I were sleeping (mind. The mother lives 5 hours away)

- had a false protection order put on my husband ( proven in court so he never went to jail for domestic violence)

The mother is VERY toxic and this is all my stepdaughter knows. She only sees my husband every three months now she comes school breaks (court ordered). Keep in mind she’s 15 but mentally she’s like a 12 year old.

My stepdaughter is VERY disrespectful to the point where my husbands family doesn’t wanna be around her when she’s here. My mother in law has pulled me aside and told me not to let my daughter whose 13 to hang around her because of it.

When my daughter is around other kids she’s a kid kid I read her messages and her friends at school they talk about kid stuff but with the stepdaughter it’s u know your mom is a bitch I’m sick of her and she tells my daughter that she’s fat etc.

I see a change in my daughter when the stepdaughter is around. Now I understand she’s a kid and gets influenced but I feel all family isn’t good family. There’s a lot more but what are u guys thoughts?

Ps. My daughter and I have a good relationship and we talk about a lot I wouldn’t say everything but she has a therapist to talk to that’s she’s been seeing for about a year now due to her self-esteem.