You know what? Of all the guys who have gone into therapy and talked about it here, I haven't seen even one who did so without at least some fear and anxiety. I was petrified when I started! It amazed me that I was even able to keep the appointment.
I doubt that the T will dismiss your situation as sibling mischief, but I understand why you feel that way. Part of our problem is that in the past our pain and suffering wasn't taken seriously; what we wanted and needed didn't matter. So as adults we continue to have that feeling that nothing has changed.
I hope you will continue to talk about your fears concerning therapy. Like I said, that's a familiar theme here. You will be talking to guys who understand exactly what you're saying, and talking about it will in itself rob that fear of some of its grip on you.
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)