Put the permethrin in a knee-high nylon and use it to pat the birds all over, under wings, between legs, everywhere. Like a powder puff. Keep it away from cats.
Ok thanks. Their bottoms look to me like they are rubbing due to itchiness, they appear to have abrasion. See how red the skin is? For the ones with open sores I would try to keep them coated with triple antibiotic ointment like neosporin original with no pain killer in it. I agree about the lice.
Some of them need neosporin IMO to stop or prevent infection.
What are the actual dimensions of the coop? Regardless of advertising, LF chickens need at least 4 sq ft of space per hen.