Nothing wrong with using nix, it's been used for many years as a mite treatment and is just as safe as Provent a Mite.
One bottle per gallon...Wipe the snakes down with it...spray the enclosure and bedding with it.
Don't put the new snakes with your other snakes and you should not get mites on them...If you have already put them with your current collection you need to treat everything!