I totally agree with BVH. All my robos do enjoy playfights (even my 3 week old babies!) but it was quite obvious when I needed to separate Bruce and Sylvester out as my other robos suddenly appeared with bleeding bums (almost like scractch marks) and chewed tails. Just keep a close eye on them for any marks.
Of course now, with hindsight, I know that Bruce and Sylvester were pregnant females (rather than males as I thought) so it was hardly surprising that they were fighting. Sylvester still has a chunk of fur missing that Bruce took out.
But on a happy note, both mums gave birth to healthy litters producing 11 babies between them.