if you want to keep more than one cock together just raise them together.... it doesn't always work but I have about 8 cockerels all living in harmony... each knows his place in the pecking order and they are by and large very happy to cohabit. We have lots of girls though, you could defo have two more with that many girls and it shouldn't be an issue. Just raise them together and introduce to your adult boy before they hit puberty. And if for some reason it fails then put them in a pot!
The other thing is that if you are not breeding you don't need a cock at all... lots to think about