I've raised quite a few Buff Orps. In the first pic, pullet on the left, roo in the middle, roo on the right. Second pic, front center and back center are pullets, back right is a roo, and I think back left is a roo too (based on feathering), but I can't see his head (i.e. comb and wattles) to be sure. Third pic, far left is a pullet, and the three lined up in front of her with red combs are all roos.
Basically at three months old the ones with red comb/wattles are roos. The ones that have very small pale comb/wattles are pullets. The pullets won't get red comb/wattles until they're about to start laying, at 17-20+ weeks.