Help needed health question

[rlong]

My girls lost their feathers on their backside belly area. I originally had flakes in their coop then went to straw and now back to flakes. I keep the coop clean. I bought a "protector" spray that is supposed to help with any mites or bugs and spray the area as directed on the bottle. Please see photo. Does anyone have advice?
Thank you in advance for any help.

 

[Kiki]

Check them at night with a flash light.
Mites live in the coop and only come out at night to eat on the chickens.

 

[kitkat5505]

My guess is mites too