it sounds like you are ready to pop from the stress of protecting your brother.... ie blowing his status in the family by revealing his past behaviors toward you. "I was young and f'd up is no excuse". at least he admitted he hurt you. so many abusive brothers go into denial and say it never happened when confronted by now adult sisters-- it makes me sick.

i agree your Dad should be informed. you may want to consider telling your Dad by yourself, as it happened to you.
Hopefully he will be supportive and then the two of you can confront your brother.

don't you think expecting your brother to come clean with your Dad is a little unrealistic as he won't even be real with you?

i wish you all the good luck in the world to bring this horror out into the open. Lancing boils is tricky business, wear your emotional armour when going into battle for truth!

who knows what your Dad will be willing to believe??? this is hard stuff to accept of one's child. remember, it will be new news to him and he will need to chew on it after his first whatever reaction....... you are gonna shake the ***** up, ya know.