Introducing questions (should I get rid of my roo's)

Those questions are really hard to answer. I don’t think there is a clear-cut "do this because it is always best" answer. You are dealing with living animals, each with its own personality. You never know exactly what they will do.

I notice you are talking about a Dark Cornish, not a Cornish X rooster, so that should work fine. Also you free range them. Having that much room makes it a lot easier.

When a rooster goes from subordinate to dominate, they can (not necessarily will, but can) change personality. If you are happy with the way your dominant one is behaving, I’d certainly not get rid of him and keep the subordinate. I can at least make a strong recommendation about that.

One job of a dominant rooster is to keep peace and order in his flock. Some are a lot better at that than others. A good dominant rooster will break up a lot of fights between flock members, but not all dominant roosters are good. During integration, these fights can be between hens, between hens and cockerels, or between new cockerels. One I’ve seen several times is between a young cockerel and a mature hen. What I’m talking about her is pecking order fights, nothing to do with mating attempts. I’ve had dominant roosters that never get involved in pecking order fights, but I’ve also had some that will break these up if they go on very long. So whether that is a benefit to you or not with your specific dominant rooster, I don’t know.

Something else I’ve seen is that a young non-dominant rooster will try to mate an older hen and she doesn’t want him to. Sometimes that hen will kick his butt herself. But a lot of the time, that young rooster is bigger and stronger than the hen. Several times, I’ve seen a hen run straight to the dominate rooster for protection when a young rooster starts acting frisky. So a dominant rooster might help control the overactive hormones of a younger rooster.

A rooster has to impress and dominate the hens for them to accept him for mating. Pullets are usually pushovers but a mature hen often expects more from her rooster. She expects him to find her food and let her have the best treats. He should dance for her and not just try to hop on. He should maintain peace and order in the flock. He should be on guard and protect his flock. Most immature roosters have not learned to do all that, so mature hens will often strongly resist mating with a young rooster. I had a 15 week old rooster that the older hens accepted without a problem, but that is really rare. This probably does not have a lot to do with whether you keep a mature one or not, just a behavior I expect you to see with a young rooster in the flock, whether a mature one is there or not. And it kind of answers your question about when a young rooster starts to act like a mature rooster. It varies a lot by the individual rooster.

How will it go with a mature rooster and an adolescent in the same flock? I don’t know. Usually the dominant rooster will totally dominate the younger one without any problem, at least until the young one matures. There is seldom any serious fighting, more chasing and running away if there is much of anything. At some point the young one may mature to the point he decides to challenge the older rooster for flock dominance. A serious fight could break out, possibly with injury. But a lot of the time, the two roosters reach an accommodation where one is dominant, one is subordinate, and they form a good team taking care of the flock, like it sounds like yours are currently doing.

I can’t see a real advantage in having two mature roosters in the flock during this process. If it were me, I’d eliminate the subordinate rooster and keep the dominant one during this process. But I can’t give you any guarantees how any of this will go. Since you are free ranging them and they have a lot of room, I don’t think you have a whole lot to worry about either way you go. You should have success.