please give me advise, nasty sister in law

I know this isn’t anyone’s business but I can’t speak to any females in my family about it, so I need other moms and female advise because I’m literally feeling on breaking point 😭

So me and my partner (same sex relationship) have been together a year, she’s taken on my little boy and he absolutely adores her. My background story is severe domestic violence with my sons Dad and the police fled me out of my home town and moved me cities for our protection, so in my head I’m a strong minded lady now and will NEVER allow someone to hurt me again.

So my partner has a 15 year old sister, she’s a bloody child ffs but she’s evil and the nastiest girl I’ve ever met. Beats her mom occasionally, smashes up her moms house and switches over everything and anything. So me and my partner have been together a year and in that year her sister has been abusive on so many separate occasions, even offering me out to fight infront of my 2 year old which is disgusting. But my partner always forgives her and I feel under pressure to forgive her for my partner and mother in laws sake. But I feel I can’t do this anymore, I love my partner so much but do I choose no drama over the love of my life. I’m currently 24 weeks pregnant (ivf baby) and since ive been pregnant her sister has had separate occasions of being abusive down the phone saying she’s coming to beat me up, calling me names, saying my partner her sister don’t even like or want me, she’s threatened twice to call social services and make false allegations to try get my son removed from my care (I’m an amazing mom) and the worst of all, said she’d kick the baby out of me, (threatening to kill her own nephew)

My partner has forgiven her once again and said it’s her sister and she needs to be civil as it’s her family. My mother in law has been texting me telling me I need to sort it out or how do I expect us all to be a family, my mother in law even cancelled to see my son on his first birthday because she said she felt too awkward because I won’t forgive her daughter. I have never been horrible, I’ve been nothing but supportive and tried to help this troubled girl. But I can’t do this anymore.

If you was in my situation what would you do? This is ruining me and my partner and I’m getting to the point where I’m questioning just leaving the love of my life for an easy life with my kids. I’ve had awful abuse in the past, I fled for a better life and I’ve got this nightmare child doing everything in her power to be spiteful.