Mites - sorry, missed this one, thanks GrandmaBird - if you are okay with using chemicals I would go to the feed store and get two things, the concentrate you mix with water and either spray or dunk them all, and the powder to put in the coop, on the roosts, and even in the run after they go to bed if you have wood chips in the run. I believe the active ingredient in the concentrate is permethrin. I used it last year when I had a hen pretty badly infested, and had no problems afterward.
I was checking on a site for mites but came across this.. It is from @gallodelceielo on our Arizona Fourm.. He is one amazing photographer & designed the treadle feeder..& the list goes on & on.. Hope this helps.
https://www.backyardchickens.com/a/poultry-ticks