Patti in Texas - Adding hens to a flock with a rooster is a whole different game than adding roosters to a flock with a rooster.
Full grown roosters will fight, and some will fight very wickedly and ugly, when new roosters are added to the flock. The new roosters will be strangers and competition males. Your original rooster sees all the girls as HIS, and he is going to very probably be very aggressive.
If the two roosters that you just bought, were brought up together, then a possible solution would be to cull the rooster that you have now, and give the flock to the brothers.
However, brothers are not guaranteed to get along, and they too may have some terrible fights. You do have enough hens for 2 roosters, but that does not mean it will be a good idea. Having multiple roosters takes a great deal of luck. Sometimes brothers work out, sometimes father sons work out, and sometimes they work for a while to have a disaster later.
Generally speaking, strange roosters do not work out, and keeping them separated but near each other just eggs on the fight. They can fight bloody through the fence. And if you are the least cramped on space, this is going to multiply the problems hugely.
Mrs K