I don't know the younger one's age, he may still be an immature cockerel. I don't know how much room you have in any coops, runs, or if you free range. I don't know flock make-up, your goals, or how you manage them. Even if I knew all that I can't tell you what will happen. With a lot of room they may be able to work it out but there is likely to be some serious fighting along the way. That may or may not break the bond between your two older ones.
How can you help them get along? Give them as much room as you can and see what happens. I don't expect it to be pleasant to watch but if they free range or have a lot of room they may work it out. Or they may fight until one or two are seriously injured or dead. No one can tell you for sure.
I think your options are to 1) let them go and see of they can work it out, 2) build a pen to isolate the boy or the two older ones from the flock, or 3) get rid of the boy or the men.