OK, try to remember that hens have been incubating, hatching, brooding and raising chicks for a million years without human i intervention. There have always been other birds in the flock. When all raised together, the mother will protect the chicks from all comers. If she doesn't, she isn't a good mother but those birds are in the minority. The other birds will definitely eat the chick starter. Most likely because it is preferable to what they have been eating which I expect is layer feed. For one, the starter is higher in protein which they may desire. It is easiest to switch all the birds to starter and it likely won't need to be medicated. For the birds laying eggs, offer them some crushed oyster shell in a separate container.
The advantage of keeping them together is that by the time the chicks are weaned, they will already have been accepted as members of the flock. Separating them and bringing them back later when the mother may no longer be in protection mode can be bad for the chicks.
