I would caution against adding birds from another person into your flock. If you are longtime friends and see their birds to know they are healthy and have no contagious diseases, it might be safe. Many can bring in a contagious respiratory disease or even something like Mareks. All it takes is one carrier. It is much safer to get healthy baby chicks from a hatchery or feed store. Many people sell chicks or pullets for money, but that doesn’t mean that they are not carriers, or have lice or mites. If you do add chickens observe them for any symptoms, and keep them quarantined for at least a month. I would separate the roosters or at least one of them. They can live separately. I have kept a roster with one or two hens, but they were very meek faverolles. If you are lucky enough to have a broody hen, you can collect some of your own fertilized eggs and hatch your own chicks. Keep baby chicks separated from adults until they are similar in size.