I keep up with the updates for this Hannah Hollows thread, so I happened to read your posts as well. First, the bare heads on the hens out side are from the rooster grabbing the neck feathers while mating. It is nothing to really worry about as long as the skin does not look raw or scabbed.
As far as your three month olds inside, I can sympathize because we once incubated some eggs that hatched in late November and it took us a while to get them out side. If they were fully feathered they could handle some cold, but you would want to make it a gradual transition to the cold weather. But you say that their feathering is not looking that great, so I can see why you might want to wait. I noticed that you said that you are feeding them cracked corn. If that is the main part of their diet, then it does not have enough protein and nutrients, so that could contribute to poor feathering. I find that it is best to feed chickens a nutritionally balanced pellet or crumble. They tend to have 15-16% protein and the needed vitamins and minerals. If you have a Tractor Supply store in your area, then I would recommend a bag of the grower pellets or crumble. It is a little early to start them on layer feed with calcium which can be started once they start laying around 20 weeks old. Of course other animal feed stores or grain elevators or farm stores store would have chicken feed, and you could ask them what they recommend. If you want more ideas on your 3 month old chicken, try starting a thread in the Managing your Flock section, and a lot more people will see your questions : )
