I the mites are white/tan, then they are likely harmless wood mites. Mites that have "fed" off your snakes will be brown or black (filled with blood). Wood mites will stay white/tan as they do not feed off your snakes.
10% Permithrin diluted 1-2oz per gallon sprayed directly in the tub and on the snakes works great for any type of mite. Just remove the water dish for 24 hours so they do not rinse it off.
I use the same mixture in my rat colony monthly to keep those pesky rodent mites away.
i'd still rather they all die. if i let them be, maybe they'll develop a taste for snake.