Sounds like you've found yourself a great new flock! I kind of hope the owners don't show up, but then again either way, you've taught your children some very good stewardship lessons!
A couple of things to address your questions about what to feed and how to house....
1. A draft free coop is very important, but it still needs good ventilations
2. The probable frostbite on the roosters comb: don't be surprised if a piece of the comb (the black part) shrivels up and eventually drops off-- this is the normal progression for advanced frostbite. Keep an eye on it for signs of infection just in case. In extreme cold weather where there might be a chance of more frostbite, you can put some vaseline on the comb--don't rub it in to the "black Part"...rubbing that part will just make it worse
3. Adding some vitamins to the water might be good to help their immune systems...some people use avia charge 2000, or an electrolite made for birds both of which are very good, however, I just put a cut up clove of garlic in their water. Garlic is a natural antibiotic, keeps the water from getting slimy, boosts the immune system, and makes your coop smell like pizza!
4. Get some good chicken feed--since they freerange, be prepared that they might not eat too much of it-so if your local feed store allows you to buy feed in smaller than 50LBS bags do so. Feed nutrients do break down, so you'll want to make sure it's used up within a couple of weeks if possible.
5. Put a golf ball in a nest box....this will act as a fake egg and with any luck, those hens will start laying in your coop instead of in the neighborhood!
Good luck, ENJOY, and have fun with your "new found family"
Sandra