Ditto to all of the above. The only time any of our boys react is sometimes if they're taken out right after girls and put into the playpen (especially if one of the girls has peed, haha), or sometimes if we don't wash our hands after handling a girl, one of our more girl-crazy males might be especially fidgety. When it comes to just housing them near each other in the same room, they might as well be on different continents.