I had something similar happen me. I was like 6 or 7 and it was my older brother mainly but it also happened with my cousin. I remember thinking this is just what I have to do to not stir the pot. I was already disliked by my family and this would only make them hate me more. I remember looking up ways to kill him too and thinking that was the only way to escape. They even caught my cousin once and then it got worse for me, I couldn’t be anywhere near my cousin but they always wanted him around not me so it was just more isolating and I felt like it was as me who had done something bad. They never caught my brother though and it just got worse but I couldn’t say anything because I felt in the wrong and like the dirty one. Even today I’ve told only my close friends and their answer is always “They were young, maybe they were going through their own stuff” Which might be true, but I was younger and what they did to me was unforgivable