I believe, as far as legal ramifications go, that there won't be any repercussions...too much time has passed (going off the assumption this was years ago) for any actionable legal ramifications to be undertaken. You needn't worry about legalities...as much as I would love to see him rot in prison for the atrocities he has committed, to be quite honest. Please try and pardon my anger there, but for him to do this to his own daughter is beyond forgiveness. I am so, so sorry you have suffered so.
I don't think your therapist will disclose anything unless they feel your brother is in imminent danger. I should say the operative word is *think*...I cannot guarantee anything without detailed knowledge of your state's laws, which is something I lack. You may wish to look into that. I do know, however, no criminal trial can result past a certain length of time...simply, too much time has would've passed for there to be any admissible evidence.
I would certainly tell them Wend...it's liberating to get such a burden off your shoulders, especially when the person you're telling is able to help you professionally. I think you'll find it to be nothing but a benefit.
Please know you're in my thoughts and prayers. I hope you'll be able to get the help and the relief you deserve.
Many hugs,
Harley