I don't have a brother.
It irritates the fuck out of me when people give answers like the one I'm about to give, because obviously the point is just to pretend you do but:
....Since I don't have a brother I don't know.
I suspect the type of relationship I'd have with him - hopefully close - would at the same time preclude threesomes. So probably not. But I think it's pretty hot from an objective standpoint.
-MGB