Need advice on combining flocks.

[roodle2]

I have 4 groups of rescue chickens (we are out in the country and my neighbor decided they didn't want their chickens any more and set them free only to have at least half eaten by predators) that I need to make into one group. Right now there are 4 roosters with 4 or 5 hens each. One rooster is very aggressive to all the others and has had several bloody fights that I had to break up. I can't see how I can keep him but hate to send him to the chopping block. Does anyone have info on how to combine flocks if I take away two of the roosters? That would leave 2 roosters who don't seem to be aggressive, 12 hens and 6 young hens about 5 weeks old who are not in the flock yet. I appreciate any suggestions.