If you put them together they will fight to establish pecking order, as will the hens and pullets. Typically, this is no big deal, although the older rooster is usually the alpha. We have 2 roosters and three cockerels and a bunch of hens and pullets, they all get along, although the cockerels were with the flock since they fledged from their mother. The only real way you will know is to put them together and see. Stay with them for a while, or go out there to watch them every once in a while over a period of a couple of days, til you see how it plays out. Most of the time, it's fine, but it just depends on the individuals. Ideally, there should be 12 hens for every cockerel or rooster, but that is not necessarily set in stone. They can get along with less. If they don't get along, you can keep the cockerel and his two pullets separate, and they will be fine with just the three of them.