How many is too many roos?

I have a flock of 13 - 3 are roosters (2 of them are 6 month old siblings - the other is their "dad"). Is it possible to have too many roos in with the hens? I've already had to remove 2 of the older hens as they seemed to be getting too much attention from the roosters and were loosing a bit of weight. Fortunately, with a little TLC they have regained their weight and health and are not integrated back with the rest of the flock. I don't want any of my "girls" to have to go through this again and would be willing to cull one of the roos if necessary. I want to breed one of the young roos next spring, and don't want to get rid of my original rooster so would only get rid of one if I need to. Other than the 2 hens getting too much attention, everyone seems to get on really well together.

 

Since I've put them back in with the flock, I've noticed that when I let them out to free range, those 2 stay back in the run. They must realise that free ranging for the others means peace for them!