are they short haired? my long haired malts like my dog! lol so it could just be dead hair falling out.. if you have males and females running around in the same area, like the boys out then the girls etc the boys can smell females which may make them fight a bit.. normally its lots of rumbling and prancing about on all fours! lol ive got meeka in my room and the boys under her so they will get used to their smell..just watch out for any marks, bites to the ears, blood etc
maybe you could mop around before you let them boys out or have a piece of lino that girls runabout on and take that up when your boys go down to play.
if both pairs are male then i doubt its because they can smell each other..