Never ever put new newborns in with older hens. The big ones will always beat up the little ones and kill them. When you set chickens together they have to be the same size.
Chickens don’t know age they just know the size. In the winter when you’re feeding whole corn, make double triple sure you have plenty of grit available at all times.
It takes a lot of grit to grind up the whole corn. De-worming your chickens is very important.
Three periods a year put a half cup of diatomaceous earth in the continuous feeder. Or use 1 tablespoon of diatomaceous per chicken in the continuous feeder. Keep the water clean.
If the water isn’t clean the chickens will get sick. Make sure the coop has sunshine and shade. And they need good privacy in the nest region and sleeping area.