@SpooknBumper if you are in the U.S. you can get Permethrin based poultry dust or spray at stores like TSC.
I would get the concentrate, a garden sprayer and the dusting powder.
Put the powder in a sock or pair of pantyhose, dust each hen with the dust. Putting the dust in the sock allows you...
You can find Permethrin based poultry dust at TSC. Depending on region, they may carry different "brands" but what I have pictured is what I have. Dust for the birds and I mix up the concentrate per package directions to spray housing, making sure to get it into nooks/crannies of nesting...
Depends on exactly which mite you are dealing with. Some may not live more than 3 weeks in the coop itself - they rely on a Host, but the Hosts (your chickens) are still there! So the life cycle continues. Mites may be able to go dormant and live up to 8 months without a host. But then...