They’re likely fine. Chickens in winter need:
Ventilation! Their coop needs to be as DRY as possible, without being drafty. So, vents up high, lots of them. Their breath and poop give off humidity, and that needs to escape. Preferably do not keep their water inside their coop. If you must, a heated horizontal nipple bucket would be best, as the water is contained.
Water They need fresh, clean, liquid water at least twice a day, if not three times. Or you can use a heated bowl or bucket and change it out every few days as it gets dirty.
Feed Your 17% layer should be fine, and adding eggs should be fine as well. The quality of the protein is of concern moreso than the amount, per se, especially when molting. Getting some animal protein in them, without going overboard, is good. If you find sardines on sale, a sardine per bird every other day is good, or your leftovers like a chicken or turkey carcass, any meaty bone really (maybe not ham, too much salt isn’t good), etc. Just make sure they have feed available at all times, especially before bed. And don’t fall for the, “Give them corn to keep them warm!” schtick that goes around every year, it’s bunk.
They almost never need heat, as long as they are dry and draft-free. I wouldn’t use a sweater either unless they truly are mostly bald, although they ARE cute.