People often keep a flock together and the eggs produced are for eating. Then when they want to breed - they pick the top two hens, and the rooster they want to hatch out of, and remove them from the flock into another set up. As it is only two or three birds, it does not have to be too big.
If the hens have been in a flock with multiple roosters - you would need to wait about 3 weeks, to be positive that the chicks from these eggs, would be the coupling you want. Then hatch those eggs. When you have enough hatching eggs, return the trio to the flock.
Separating roosters can cause a problem when you go to reintroduce the rooster back into the flock. I suggest, just pulling the hens of choice and separating them leaving the roosters with the remaining flock. Keep checking the eggs for fertilization - when you get clear eggs for a couple of days - then add the rooster of choice. You might try, adding the rooster in the early morning, and returning him to the flock in the late afternoon, so reintroduction does not become an issue.
Keep checking the eggs until you see the bullseye-then start collecting the eggs for a clutch to incubate. You should have a good hatch rate if you keep your eggs for about 10 days. Older eggs after that, tend to loose hatchability.
Mrs K