You can never tell for sure what will happen with living animals. That's just part of them being living animals with their own personality. Many of us raise cockerels with a flock that has a dominant rooster. Many have multiple adult roosters. Do disasters happen? Of course, you are dealing with living animals. Do disasters always happen, no, chickens are not extinct. If roosters killed all male chicks they would have long been extinct.
One of the ways to make it more likely that they will get along is to raise the cockerels together with the flock. That can be as siblings or with a mature flock-master rooster. The more room you have the more likely it is to be peaceful. The more crowded it is the more likely you are to have issues, some really serious.
In the wild the normal sequence of events is that the dominant male runs the cockerels out of his flock when they reach a certain level of maturity and start trying to breed his hens. The boys form a bachelor flock until one matures enough to carve out his own territory and and tries to attract females. Or maybe he challenges another rooster, his dad or another one, and fights to try to take over the flock.
But your chickens are not wild, they have been domesticated. If you have enough room it is possible they will follow the "wild" model, but most of us don't have enough room for that. It is possible they will fight to the death. But it is also possible that they will reach an accommodation, knowing which is boss but working together to take care of the flock. I've seen roosters split the flock into harems. I've seen roosters be best buddies and hang out together all day. The hens still get fertilized.
Most hatcheries use the pen breeding method. If yours are hatchery birds that's probably the system yours came from. That's where maybe 20 roosters are kept in a pen with 200 hens to get fertile eggs. They have more room than many broilers or laying hens kept commercially but they are in one large pen, not as much room as you might think. They may spar or fight to determine which is boss but they don't kill each other that often. Is it guaranteed that yours will kill each other? No, no guarantees. I'd still suggest you have a plan B, a pen ready where you can put one of them if you feel you need to.