My cousin raped my older sister when we were kids and i just found out. What am i Supposed to do

I just recently found out that when I was around 7-8 years old my older cousin(m11) raped my sister(F10) For context I only communicate with my fathers side of the family. None of us talk to our mother side because of numerous horrible things theyve done to my family. Im not really sure if all of it is appropiate for this channel so ill keep it mostly ab my cousin. I dont remember how it got brought up but i was talking with my sister “reminiscing” ab all the crazy stuff that our moms side of the family did and eventually she got really quiet and told me about how when she was little He asked to see her private parts and it escelated from there. My Father knows and im not sure if my moms does. I get he was only 11 and i can only imagine what happened to him even earlier on in life growing up in that household to make him do those things. And Even though it was over 10 years ago i cant stop thinking about it. This guy gave me his entire Skylanders collection when he outgrew them (iykyk) He was my older cousin, the closest thing i had to a brother, i idolised him. We cut off ties to that side of the family a few years after the incident so by the time i found out, he had already graduated college and is long gone from our lives. My sister seems to just want to forget it ever happened and im going to respect that. My dad seems to be in the same boat, which im proud of him for controlling himself but i think part of me also resents him for not doing anything about it. Late at night i will find myself staring at the ceiling just listening to the ac rattle thinking about all the things i want to do and say to them for hurting my mother, my sister, and me. I will be honest i was the most protected out of my family so it feels wrong for me to be mad for them but how am i supposed to move on from this? Its eating at me from the inside out.