If they are living together then they will eat what ever food you put out. Separating them is the only way to be sure that the non layers eat only low calcium feed. You could feed them a starter/grower or flock raiser with a calcium supplement on the side. There are feeds formulated for roosters out there. Some never feed a layer because they always have a mixed flock. If you free range or give a supplemental feed like table scraps or scratch, then the level of calcium is much lower then just straight layer. Adult birds can tolerate calcium better then chicks. It may take years for a detrimental effects to show up, by then the rooster has most likely died of something else. A lot of keepers take that approach.
