Are any of the chickens eating the feathers?
How many chickens do you have and what is the size of their coop and run?
If they are eating the feathers you have a problem with lack of protein in their diet.
A minimum of 4 square feet per chicken is needed ( I don't think that's enough personally)
Just to be on the safe side I would dust everyone with poultry dust to get rid on any lice or mites. I would also increase their nutrition. Give scrambled egg, cottage cheese, yogurt, chopped greens, a little fruit (can cause diarhhea) and vegetables. Don't give all the treats at once, rotate them and don't overdue it.
If you don't have poultry vitamins purchase some. They are in a powder form and you just mix them with their water. If you think they have a protein deficiency purchase a quality dry cat food. Give each hen 4 or 5 pieces each day for 2 or 3 weeks. Don't use dog food because it gets it's protein from grains and cat food is made from meats.
None of the above can hurt. It's worth a try. You certainly have well fed, healthy chickens going in to the winter.