You will need to keep them separate. They will be sexually active LONG before your pullets will be ready, and 4 will more than likely be merciless. Truthfully you need a bachelor pad or cull all 4 of them.
If you have a multi-generational flock with older birds that are bigger than the cockerels, or truly have a VERY large set up, then multiple cockerels can sometimes work in the flock as a whole. But if I read your post right, these youngsters are your only birds. The cockerels will get bigger faster than the girls, and will begin to bully them.
Often times, a cockerel raised with just flock mates, will become not only a bully to them, but can become human aggressive. If you have children under the age of 5, I strongly recommend you cull them all. If you are asking for advice, I recommend a hen only flock the first year, especially if you are truly in a back yard set up or have children sharing the yard. Roosters take some experience, and many people vastly underestimate the violence of a rooster attack. For a child, it will be at the level of the face.
Once the pullets begin to lay, look around for a mature rooster, as close to a year old as you can get. You will get a much better rooster. People often have a rooster that was an extra, that was so nice, they did not cull him, that is the rooster you want.
If you make a bachelor pad, you can watch them develop, and often times make a better decision as which is the best rooster. Do check SOP for the breed, check legs and feet that are straight, beaks that align, and other characteristics for the breed.
Mrs K