My sister told me she was molested

I NEED TO VENT!!!! I WANT TO HELP MY SISTER!!!!

have caught my sister touching on another kid he was 6 she was 11, this wasn’t the first this happened it happened before but she came up with an excuse, it didn’t make sense but I didn’t wanna believe my sister was doing something wrong, I cried that whole day mind you yes I was older then them about 15 but I didn’t know what to do nothing happened for a while till I caught her again to the boy(our cousin) i brought him in another into another room and talked to my sister. When I was younger I was molested my an uncle and my dad and raped by my cousin all under the age of 10, so I was very emotional when I seen what was going in I was crying and asked her where did she learn that from she keep saying she didn’t know then she said that’s he learned about it at school, I didn’t question it much I just told her to please not do it again and I told her to tell my step mom what she did when she had the courage. The next day I asked if she told her she said no, I was kinda sad but I didn’t want to tell on my sister I just told my sister if something happens at school again to tell me or tell our step mom, ever since she hasn’t done nothing wrong. Also my dad still around us I’ve never told nobody besides a cousin what he has done too me, my sister final told me it was my dad who was doing stuff to her I was so heart broken I wanted to kill him I felt terrible because that’s one thing I never and I mean never wanted one of my sisters to go through I went around and asked my other sisters they said that he didn’t do anything to them I questioned my sister more about it and what he done was exactly what he done too told my step mom she didn’t believe my sister but she had to tell dcs my dad can’t be around us gladly and my step mom so anger at my sister because she believes she’s lying but I know shes not. I will never mention what happened to me to anybody besides that one person who knows but I feel like I failed my sister she always so angry and depressed I just want to help her so she won’t end up in a lot of different places I was in for the same reasons