If you incubate and brood them inside, I don't see why you shouldn't hatch winter babies. Your biggest problem may be getting enough eggs in the middle of winter. They will be completely feathered out by the time you put them out in the coop and since you have other birds already you could, perhaps, divide the coop so the new birds are partitioned off from the others. That would protect the younger ones and protection, yet the older ones would have a chance to get used to the new birds.