Facing a crossroads

My SO and i have been together for a total of 10 yrs, married for 8 of them. He recently got temporary custody of his eldest daughter and it started out pretty cool. I was laid off and making sure she got what she needed on my own without the help of her dad. She began to ask questions about how we met and got married and i brutally honest. She formed her own version of the events and began telling my in laws all these lies. With out them ever co.ing to talk to me or my husband about these lies they fed into them and recently it just literary blew up. She began breaking into our room and helping herself to my personal belongings, she put old food in her dresser drawers, refused to go to school and counseling. So when her dad aaid he would send her back she call his mom and sisters saying thta csb was on the way to take her back. They show up at my home 10 pm yelling and causing a ruckus. My inlaws totally was disrespectful toward me amd he said nothing. His daughter did the same and still nothing. The holiday came and i refused to go to his family function due to what just transpired. Because i didnt go he didnt go and i told him he should go anyway. Well Sunday morning i get a threating text message from his siblings saying that im the cause of all the issues this child is having, im keeping the rift between her amd her dad, and when i give birth they were going to fight me. Im a grown woman and had no say so as to what her father decided. I did nothing but accept this child and try to do my best to accommodate her and her needs. I don't how i became the bad guy but now im totally done. I want nothing to do with this child, or his family. I am at a loss and feel like this child is purposefully trying to rip my marriage apart or try to make me stress to the point of loosing my unborn child. Now i have a constant attitude towards him and say nothing at alk to the child. Im in need of outside opinions, and if you have read this in entirety thank you.