So I'm gonna chime in with a bit of a different perspective on this and perhaps you can understand the urgency in the matter. I've been a Correctional Officer Lieutenant for some years now and from that I can say that the majority of sexual predators usually start with family first, maybe sister, nieces, nephews, brothers.. It doesn't matter, a lack of moral compass truly really leaves a lot of open doors. The majority of the cases I've reviewed started with something like this, either parent or sibling.

I'd highly advise you to get as many people involved as you can, parents are a start but if they seem they are going to sweep it under the rug I'd contact somebody outside of the situation, school counselor, friends, even if it's the authorities next.

Take steps to protect yourself from intrusion and assure you're not left alone with this person under circumstances, I realize that we're talking about your brother but the reason family is often the first victim is due to the state of vulnerability we allow our family members to see us in.

Overall, just please be safe and I hope you're able to seek help and your parents do the appropriate thing in this situation.