It's toxic to all animals, especially birds and cats. It's even toxic to you and me in the right amounts. Onions, garlic, etc, can harm anything in the right amount.
Nix the DE, it doesn't really work for mites and is pretty bad for you and them to breathe.
If they're not all laying, it doesn't...
Garlic won't do a thing and can harm them as it's toxic to birds.
Possibly ivermectin but let me look.
Can you add permethrine powder to the sand now? Some mites are tough and requires elector psp.
Mites can cause low egg production.