Check the coop and the birds at night with a torch, if it is red mite they will be crawling in them and you will notice them all over the coop and perches, they are far more active when it's dark, if you can see a heavy infestation in the day then it must be bad, that is if it is red mites, from your description it sounds like it, do you have any where else to keep the birds while you thoroughly clean their house with boiling water and vinegar? you'll need to remove perches too as they tend to congregate around the ends and under felt roofing, if you have felt rip it off! I would be wary about using any other chemical sprays if you keep bees, you can also treat the birds with drop on ivomec but you can't eat the eggs for 2 weeks if you do, if the birds have nice red combs I wouldn't bother.
