The 1st set is 4 months old, and the 2nd is 3.
Two immature cockerels. It sounds like at least one is hitting puberty. It is still a long way from being able to determine how either will act as a mature rooster. Each individual chicken (male and female) has its own personality. Each flock has its own dynamics. That dynamic can change as you add or subtract individuals or as chicks mature into adult members. The personality difference between an immature cockerel and a mature rooster can be huge.
Your flock has mature hens. There are several different things that could possibly happen as a cockerel matures in your flock.
As he matures everything could be calm and peaceful. Not much drama. After he reaches a certain level of maturity he takes over as flock master and the dominant hen lets him. No drama is unlikely though. He may try to mate the pullets his age and leave the adults alone. He may try to mate the adults. Some may let him, some might run away. Some may fight him and chase him to beat him up. Some, especially your dominant hen, may knock him off if he tries to mate a pullet or another hen in her presence, even if that pullet or hen squats for him.
I think having more room helps improve your odds of things being more peaceful but it is certainly not a guarantee. Sometimes there is very little drama, sometimes a chicken gets injured or killed, most of the time what I see is some drama but no one really gets hurt.
I typically raise 20 or so cockerels with my flock every year, along with a similar bunch of pullets. With that many cockerels there is some drama every year but after I thin them to one that will become the flock master there is usually very little. One year though the fighting between the one cockerel left and the head hen was vicious. I have over 2,000 square feet available for them during the day, which I think helps. Most years the drama is not enough to bother me. But every three or four years it reaches a level that I isolate several cockerels in a special grow-out area to keep relative peace in the flock.
You only have two cockerels and you plan on getting rid of one this weekend. You need to pay attention as he goes through puberty and becomes a mature rooster. If you have as much room as I think you do things may work out well but you may need to isolate him for a while.
People really get hung up on breeds. I don't put any faith in breeds as a guide to personality, especially from hatchery birds. Some breeders but certainly not all breeders may breed for personality. Many breeders are breeding for appearance instead. Hatcheries are not known to breed that much for the personality a breed is supposed to have. Some might some, every hatchery has its own person who decides which chickens get to breed, but from what I've seen personality is usually way down on that priority list. If you read enough stories on here you will find a rooster of any breed that is a terror and one that is a saint.
You will find that the ratio of boys to girls is pretty meaningless too. You can find a flock with one rooster and over 25 hens where some hens are over-mated and barebacked. You can find flocks of one rooster and two or three hens where they don't have any of these problems. The key word here is "rooster". Immature cockerels and mature roosters usually act very different. Most of the horror stories you read about on here involve immature cockerels, not mature roosters. But with living animals you can always find an exception. I don't expect the exception to be the norm. I'll also repeat the space component. You will find a lot more bad behaviors when they are in tight spaces than when they have room to spread out.
Which one do you keep? That is purely your choice, not mine. They are too young to go by personality so what traits do you want in the offspring? They are both red which means the hen's genetics will have a lot to say about what the chicks look like. I'd put them about even on that.
Murray McMurray hatchery says they select Ameraucana breeders based in egg color, not feather color. Their Ameraucana flock was established before Ameraucana were even accepted in the US as a breed with breed standards. I find it refreshing that a hatchery is honest about that, many are not. So I would expect the Ameraucana's pullets to lay blue or green eggs. The Rhode Island Red's pullets should lay brown. Murray McMurray did say that occasionally one of their Ameraucana pullets do lay brown eggs so there is always a chance but I think your odds of getting blue or green eggs are really high.