jojo, some of the questions you are asking are addressed in the posting/thread entitled if it feels right.
I think you are doing the right thing in seeking counselling and making sure your sibling's needs are being looked after. I think the latter is a particularly responsible and courageous thing to do. It shows, despite any doubts you may have, that you are owning up to any responsibility you may have had in causing your sib's pain. If your sibling is male, you might consider referring him to this forum.
As for your own abuse, you, by your own admission, are somewhat vague as to the details so it is hard to really offer an opinion.
I just read a quote from mikechurch
in another thread, it was describing his life on the streets, and might be the best definition of whether abuse is taking place or not.
there were winners and losers in every sexual contact
In other words, if there is a winner or loser in a sexual encounter. Then almost certainly there has been a perpetrator and victim.