As others have mentioned, don't stress too much yet on the skin. Do get the PAM as suggested, and soak for about 15 min daily in warm water to ensure he's hydrated. Treating too heavily for mites while he is weak and stressed can cause more problems than it solves.

I personally would also pick up reptile relief to treat the snakes themselves with as well, but again, would wait on the male until he's in a bit better shape - the females you can probably treat ASAP.

If he is willingly eating, then soaking him once a day in the water should not be too much of an issue for him. It should also help hydrate him, which in the long run will help get the skin off. Give him 5 days, offer him the mice again, then if he takes those go on to small rats. From there, once he poops, offer him what you'd offer him normally if he was at a good weight.
I've rehabbed a few scrawny, skinny, abandoned snakes over the last few years (including an imported male that refused to eat for his owner for almost a year - 4.5' snake that weighed just under 800 grams when I got him)...once you get them going, start with small meals, let them put on a bit of weight, then just go to the size prey item they'd be eating if they weren't so wretchedly skinny. Starting small helps get their gut going, and once that's ready and passing food, you can feed them like a normal healthy snake and you'd be amazed how quick they go back to a good weight.

Good luck with him!!

-Jen