It won't take that long for mites to kill the snakes...trust me. Mites reproduce exponentially...just because the snakes look OK now does not make them safe.
And it would help if they had a bowl big enough for each of them to soak in, to drown what they can, relieve the bites, & importantly (!) to stay hydrated. Two
bowls would be better, since there are 2 snakes in one cage. If they cleaned their cage daily & gave each snake a supervised soak in water (NOT for drinking!)
that has a drop of dish soap added (to break the surface tension so mites drown easier) for 20 minutes a day it would help, without added pesticide risk, but
ultimately they likely need something more (like Provent-a-Mite) as well.