How was it determined that your birds have MS?
If in fact they have cocci and the corid isnt working, treat them with sulfadimethoxine or sulmet. You'll need a prescription from a vet for either of these products.
Just to let you know that if the sulfa drugs dont work, capillary worms can cause blood in feces and you'll need to worm your birds with valbazen or safeguard.
Scaly leg mites can be treated by putting vaseline or vegetable oil on their legs for a long period of time until healed. Burnt motor oil works well also.
So much for DE and wood ash. Depluming feather mites treatments, read post#2 in this link: Good luck.
https://www.backyardchickens.com/threads/depluming-mites-please-help.414354/