Hey OP I love your stories so far, I have had a couple of similar situations, but like the one with your brother it was with my little cousin, and it was weird because I have nothing but male cousins and for some reason me and two of my cousins one 2 years older one same age, would go back and forth with each other, but we would all kinda force ourselves on our younger cousin. it stopped when we were all about 12 or 13, but none of us have talked about it since.
I would love to hear more of your stories and I'll tell you mine, whats your email?