They look like sticktight fleas to me-- Ace6558966
Maybe this link will help you:
https://www.backyardchickens.com/t/431533/please-help-stick-tight-flea-i-think
The mites won't go away if you just dust the litter in the coop with desired mite/lice dust. You need to clean out the whole coop. They'll crawl in the cracks and crevices and hide and reproduce. (Very rare cases have been resistance to mite/lice dust)
If the mites are bad on the hens, you...