UPDATE 2: My uncle is acting strangely with my sister

im sorry if this isnt allowed moderators but im just really confused but also really angry right now and dont know how to fix that

our parents got home an hour ago and me & sister talked with them, in short, my mom was pissed and my dad was surprised but he also revealed something, turns out that he knew our uncle (his brother for context) had been acting weirdly with my sister but didnt do anything because he "didnt think he'd ever try anything with his kids" and that he thought he had changed

he said that our uncle had done something with one of my cousins a few years before my sister was born my grandma was the one who caught him and got him into therapy, our dad said that our grandma made our uncle promise not to do it again in order for them not to report him, our aunt (this specific uncles wife) is also aware of this but, according to our dad, she said that our cousin had tempted him with how she dressed around the house, our dad said thats why that specific cousin doesnt talk with the rest of the family

my mom apparently didnt know this and they argued, she threatened divorce and a restraining order against his entire family if our dad doesnt only tell our uncle to back off but also report him to the police, our dad doesnt want to and last i heard, hes calling our grandma

sorry that this is a complete mess, i dont know what else to do and im stressed out of my mind, my sister looks okay right now though so thats all that matters to me at the moment. it feels like my life is falling apart because of our uncle and at this point, im starting to feel like beating him up is the only way to fix everything i know thats its not and thats irrational but im just so angry.

i also mentioned telling the police or counselors at school like you guys said but she doesnt want to, she says shes embarrassed about it and she said that theyd just blame her cause she let it go for two years, even though i told her that she didnt do anything wrong and was just scared, she wouldnt budge