To make it work, think along these terms. More mature chickens outrank less mature chickens in the pecking order. If the less mature invade the others' personal space they are likely to get pecked. It usually doesn't take long for the younger to learn to avoid the older. Sometimes the more mature bully the young away from food or water. Does this sound like what you are seeing?
I'm not sure where they are all sleeping now or what your coop looks like. The bigger the better. I manage this in two different ways but only one would apply to you as you did not raise the chicks in the coop. For the chicks in my grow-out coop I let them do a "see but don't touch" (can see each other across a wire fence) for a week or more, then I turn them loose. Mine technically don't free range since there are fences but I have over 3.000 square feet available to them so it is pretty close to your free ranging. They quickly learn to form two separate flocks. The younger avoid the older and they sleep separately at night. I have several food and water stations scattered around so they can eat and drink without being bullied off. Each group is different. Sometimes they intermingle more than others but usually the younger just avoid the older ones.
After they have proven to me that they can coexist without harming each other (usually around 1 month of roaming together) I move the younger into my main coop. The way my logistics work out that's usually around 12 weeks of age but I have had some groups merge sooner. I wait until it is dark and lock the younger in the main coop with the adults, then am down there as they are waking up to make sure that everything is going OK. I have a fairly large coop (8' x 12') and places the younger can get away from the older. I don't worry where they sleep as long as it's not my nests and is predator safe. I do this so often that I put up a juvenile roost separated from the main roosts by a few feet, lower than the main roosts and higher than my nests. I do not try to force mine to sleep on the roosts with the older ones, they will take care of that when they all mature. I'm set up for this so it works pretty well.
Excellent idea.
Since yours free range two males might work, it does for many people. They need to get through puberty which can sometimes be pretty rough, both between the boys and sometimes on the girls. You may or may not need two separate coops for them, traction varies on that. I'd have a way to immediately separate them if necessary, the need may come up very quickly.