Raising them together helps. That's either as siblings or as father/son, even if they are not blood related. But that is not going to solve the problem. They still have to go through puberty.
When the hormones hit the immature cockerels those hormones often take over. The hormones tell them to be dominant so they are ready to fight other males and possibly dominant females. The mating act is an act of dominance, the one on bottom is accepting the dominance of the one on top either willingly or by force, at least temporarily. With immature cockerels that's usually by force. All that mating you typically see with immature cockerels is not about fertilizing eggs, many times the girls are not laying. It's about dominance with hormones out of control. As someone once said, watching them go through puberty is often not for the faint of heart. The fighting and the mating can be pretty vicious. A lot of cockerels literally lose their heads in this phase.
At some point the cockerels can mature enough to challenge a mature rooster. Until they reach this point they typically just run away. Sometimes the older one wins, sometimes the younger one does. This might be a fight to the death or one may decide it is better to run away than to keep fighting. Sometimes one fight is enough, sometimes it takes more. Sometimes you never see any fighting, the older one wins by intimidation.
Often, if they live through this phase, the boys reach an accommodation on how to care for the flock. If they have enough room they might each claim a territory out of sight of the other and collect whatever harem they can. The hens decide which male they like best. They can work out other ways where they stay more together. Each chicken has its own personality, each flock has its own dynamics. We don't always see the same thing.
The only thing I know that can improve your odds of getting through this is to give them as much room as possible so they can run away if they need to. Forcing them to stay near each other does not help. And always have a Plan B in case it doesn't work. That generally means have a place ready that you can isolate one on a moment's notice if you have to.
Good luck!