Well the hens could be over mated or whatever and the 2 roosters might fight. It also depends on if you free range or have them in a run. If you free range then 2 might be fine since they have lots of space.
Okay well if they are raised together and such they may not fight because they know each other and such. But if they are going to fight then they are just going to fight no matter what. Unless you keep hem separated.