Can you post any pictures of the chicken’s bottoms in case of feather picking or broken off feathers. I have used BluKote on red skin to discourage pecking. My polish hens’ head feathers would be pecked, but BluKote stopped it if started early. Mites in a coop are a nightmare, since they can hide in the cracks and crevices at night. Some mites are on them night and day. Permethrin is good, and I like to use Martins or Gordons permethrin 10 concentrate diluted in water 1 tsp per quart of water. Use a spray bottle or garden sprayer for the coop. Prozap garden dust permethrin may be more tolerated, filling a sock to dust your chickens. Mites hatch every 5-7 days, so start treating every 7 days. Consider pressure washing your coop, and then spraying it with the permethrin. Some people have been so desperate with mites, they have heat teeated the coop or switched to a plastic coop. I have used permethrin for lice, but not mites. Repeat treatment and consistency is key. Straw is something they can hide in or be brought into a coop on, so I would avoid using that for bedding. Good luck on treating them. Consider Elector PSP or talk to your vet if permethrin doesn’t help.