Someone I know has had a run in with siblings who are gay (batted for opposite teams though) so this story seems like something that could really happen and does probably happen among the gay and straight community.
I really liked Colin and Peter. They were adorable and Peter was just so fun and easy going. They balanced each other perfectly. Mark was a bit annoying to me. He came off as a pushy jerk, almost childlike in the belief that he was irresistible and that he could have anyone he wanted on his say so.
The thing with Mark and Peter's mother was a bit sad (both in that they never got her to accept them for who they were and that she was ill and well you know...).