Why do you want a rooster? What are your goals involving a rooster? The only reason you need a rooster is if you want fertile eggs. Anything else is just personal preference. Nothing wrong with personal preferences, I have a few myself. But that is a want, not a need. I generally suggest you keep as few males as you can and still meet your goals. That's not because you are guaranteed more problems with more boys, but that more problems are more likely. Not knowing your goals I think getting down to one is a good idea. You may eventually decide zero is a better one, but that is totally up to you.
What are your goals involving a rooster? Which one best meets your goals? It doesn't matter which I'd chose, that's my goals. What matters are your goals so that has to be your choice. That could be based on appearance, behaviors, or other things.
As far as behaviors go, you have a problem. To start with you don't have mature roosters, you have immature cockerels. You probably have immature pullets too instead of mature hens. I don't go by the calendar for that, I go by their behaviors. My pullets mostly act like mature hens about the time they start laying. I wish it were that easy with the boys. I've had a cockerel start acting as an adult at 5 months. That's rare, it's only happened once. I've had one go 11 months before I considered him mature, some people on here say they have had some go longer. Most of mine seem to grow up at around 7 months but it is very much an individual thing.
When they hit puberty, which it sounds like one of yours may have, their hormones take over. At that stage the mating act is about dominance, not about fertilizing eggs that probably aren't being laid yet. The one on bottom is accepting the dominance of the one on top, either willingly or by force. It's usually by force. Until they mature the girls don't want to be dominated, especially by immature brats. So they run away. The boys usually chase and force the girls. I don't know if you are seeing this behavior yet or not, but get ready. It can get hard to watch. Once the boys and girls mature it usually becomes a peaceful flock but getting to that point can often be challenging.
The boys determine which one is dominant. Maturity has a lot to do with that. The more mature will dominate until the other matures. It may become fighting, it may involve more running away and chasing. It can be a fight to the death or they make get along great. There are no guarantees when it comes to any living animal's behavior, each is an individual. That's part of what makes this so hard to write about.
The dominant cockerel or rooster will often suppress the behaviors of the less dominant. The flock master has certain responsibilities in taking care of his flock. The dominant one often doesn't let the other one do those things involving peace and security in the flock, let alone mating. Sometimes the competition drives one to excesses in behaviors.
What I'm trying to say is that it is really hard to predict how a certain boy will behave when there are others around. It's much harder when they are so immature and have a lot of growing up to do. I wait longer than 4 months for sure and still don't always get it right. Sometimes neither is a good choice, sometimes either is.
So what can you do? If you are in love with one, you've made your choice. Go for it, there is a fairly good chance it will work out.
You can let them go as they are for a while. Something might happen that disqualifies one. As long as no one gets hurt (you, your family, the pullets, or either boy) life is good.
You say you can't separate them. I don't know your conditions but I'd think about that. If the behavior goes horrible, and it can on the spot, what will you do in an emergency, even if it is just overnight. A dog or cat cage or crate, an outbuilding, just have a plan. It doesn't have to be permanent, just something to give you a chance to handle it.
I know this is long-winded. The bottom line is that there is no easy right answer that works every time. At some point you have to make a choice and live with it. Usually it works out but when dealing with living animals you don't get guarantees.
