I never found Rosy Barbs to eat BBA. I had 5 of them during a huge bloom of it and they never even looked at it. First time I've heard of that. As for the SAEs, they honestly didn't touch it either :-/ I ended up throwing away the plants it grew on, removed the driftwood it grew on, and started adding faster growing plants. That seemed to prevent new growth.
As far as SAEs being aggresive with each other, I've never seen this. They are a social fish and should be kept in a group. I have 5...well 4 after a jumping incident this weekend :-( They're constant companions, moving as a whole group from one plant to the next, and I have a mix of both genders. It' really a bad idea to buy fish jsut to eat algae. And like I said, those SAEs belong in a happy group with plenty of room to swim and play together.