TW : mention of domestic violence

Throwaway account for obvious reasons. I’ll try to be concise and clear but I feel like a total mess right now. My (29 F) little brother (18 M) Thomas recently moved really close to me with is new girlfriend Lilly (18 F) to start a new life has a grown up I guess. We weren’t really close has I left home really young and the family dynamic was messed up. I moved pretty far away and was able to see him and the rest of my family less often but stayed present by being in touch. I did my best knowing that he has been through a lot as a child and he was suffering a lot, but growing up, he became more and more violent and the situation got out of control pretty quickly. Anyway, last year, I had to move further away. He’s behavior was starting to improve, according to my family. He had then met his girlfriend and things moved pretty quickly. She is from a very religious family and had to cut contact with them to be with my brother. They decided to move next to me and he’s suddenly back in my life, full time. I was worried about her since day one, because he didn’t even try to hide he’s behavior in front of me. He called her names, belittled her everyday and the physical abuse came quickly after that. I immediately did my best to help her. I was a victim of domestic violence when I was younger and I just knew I couldn’t force her to leave, because she didn’t wanted to. But I never stopped to show her that we (me and my SO) were there to help her, that there were victim support and tried to stay present because he isolated her pretty quickly and she had no one to go to. She did leave him a couple of days ago and my brother is furious, like really crazy mad at me for just being there for her, but that was expected. But now some of my family members are mad too ? Like my dad is mad at me. He says I’m being fooled by a manipulative kid (Lilly, who he only met like twice). My dad. That my brother has already hit. I feel like going crazy. I can’t sleep, I having breakdown after breakdown, and I’m scared she’s going back to him, I’m scared I haven’t done enough. And now my family doesn’t even want to help. My mom is in a big fight with my dad because of what he said to me. Everything is a mess. I feel like deep down I know that I’m doing the right thing but I’m starting to wonder if to the outside eye it seems like I don’t.