Oh, you snuck in another chicken. That’s 13, not 12. Still, that number doesn’t change things but two males might.
You only need three nests for eleven hens but an extra doesn’t hurt. Six is really overkill. You might save yourself some materials and construction time by only providing four. Depending on how you do your nests they sometimes take a fair amount of construction and might use some fairly expensive hardware.
That’s going to be a lot of room, your pullets will love it. The question comes in with the cockerels. Sometimes two males get along great when in the same flock, sometimes they don’t. Especially in adolescence they will determine which is boss, probably by fighting. That may be serious fighting, it may mostly be running away and chasing. It’s just something to watch for, you may need a plan to handle it if they can’t get along. Without even considering integration, expect a lot of drama down there when the cockerels and pullets go through puberty. The age difference in the two groups may add to that a bit.
So how do you integrate 14 week olds with 10 week olds? Start out buy housing them side by side for at least a week. They need to get used to each other so they don’t fight just because they are strangers. The older chicks will dominate the younger anyway, so it would not really be fighting. The older would beat up the younger and the younger would try to run away.
After they have gotten used to each other, allow them to roam together during the day. Weekends are usually best but some time you can be around to observe and act if it gets too physical. It’s great if they go to different places to sleep at night as long as they are predator proof. There is probably enough age difference that the two groups will form two sub-flocks, soon get to hanging out in two separate groups but being peaceful as long as they stay separated. Forcing them to stay close to each other can cause bullying and lead to injury.
Having separate feeding and watering stations helps a lot. One way the older intimidate the younger (chickens are natural bullies) is to keep them away from food and water. Two or three feeding and watering stations destroys that strategy. It also helps to have places the younger can hide behind or under. Don’t create traps where they can get stuck and can’t get away if they are attacked, but just breaking the line of sight can help avoid conflict.
Another good thing to have is some place the younger can perch to get above the older. It’s pretty common for my younger ones to be on the roosts when the adults are on the ground when they are all locked in the coop. The younger are just avoiding the older. They like to perch anyway so something they can get up on is usually a good thing to have.
The time mine are most cruel to each other is as they are settling down for the night. Where they get to sleep is based on the pecking order. The ones higher in the pecking order (your older ones until they all mature enough to form one flock, usually when the youngest start to lay) get to decide where they want to sleep and can be pretty vicious about enforcing those pecking order rights. What I practically always see is that the younger will not sleep on the roosts with the older until they mature because they get beat up. In the meantime they look for a safer place to sleep. That might be your nests. If you have a lot of spread out roosting area it may work out but I ran into that problem so much I wound up putting in a juvenile roost. It’s a little lower than the main roost and horizontally separated yet higher than the nests. If your younger ones start sleeping in your nests you might consider something like this. Or if you are going to be adding more chicks later just build one now.
The more room you have when you try to integrate the better. That’s in the coop as well as the run. That’s even more important when you have younger ones going through puberty. The issues you are most likely to see are probably going to be more about puberty and those two cockerels than actual integration. My first step would be to figure out how to house them side by side for a while. A separate coop/pen where you can isolate a chicken often comes in handy anyway. Get your expansion done and then go for it. With that kind of space you have a great chance for it to work out. Good luck!
