You have a mega infestation. You have to sort all hen houses today.
1. get your old clothes on you can throw away after.
2.get some rubber gloves and a
dust mask/ safety protective face shield
3. Burn all the straw and bedding.
4. Net-Tex Total Mite Kill Concentrate 500ml Ref: NTX4354...Price: £9.95 ..Contains: Permethrin 2.3%, Tetramethrin 0.23%, Benzalkonium chloride. Do not spray on birds or animals, avoid contact with skin.
5.
Add 100ml of Nettex Total Mite Kill Liquid Concentrate to 1 Litre of water.
6. Add to an Old mop bucket and mop all the houses and sheds, in the roofs , whack the mop head in every crevice. Watch your eyes don't get splashed and keep off your skin. My arms are still dry and sore where I splashed them..
7. Leave it for 2 hours.
8. 1 drop of Ivermectin on hen neck on skin for every bird.
9. Don't eat the eggs for a bit. I gave them to my pet pig. Hes been treated already but any residual ivermectin that is in the eggs wont do him any harm.
10. I hose blasted the fence panels down or any wood near the hen houses but it doesn't matter!
11. After 2 hours sprinkle the Diatomaceous Earth in the hen houses everywhere, roof and edges of floor. On all the floors then put saw dust over it and let it air for a while.
12. Dust the hens with net tex total mite kill powder which is just Diatomaceous Earth, on the backs, tail and feet.
13. If you have lots of hen houses maybe a Net-Tex Total Mite Kill Concentrate 2 lit which is £32. I spent £200 last week on it all and know they have gone but I'm sure I exterminated them, unless some are hiding but according to my vet who said burn the lot, but the powder will kill any stragglers.
14. Make a dust bath for the hens to sit in. Put more Diatomaceous Earth in it, just leave near hen houses. Plastic tray...
15. Strip off and burn your clothes or bin them sealed in bags and have a good long shower.
If I lived near you I would come and do it for you. If any other of your hens are lethargic and not eating then they are anemic. I tried to use a dropper and liquid that gives the hens energy, vitamins and protein, cant remember what it was called but it didn't work. The hen died.
Good Luck...