heres what you do when you have mites:
take everything out of the cage, subsrate and all, clean the tank. use paper towels for substrate, put in a plastic water container and plastic hide boxes, and basically follow the directions. ive only ever gotten mites once, and i used a powdered mite killer, and sprinkled it under the paper towels, and the mites were gone two days later. and also, its not a good idea to house your snakes together, its very stressful on the snakes since theyre solitary animals. and if one gets sick/infested, they both do. they can also fight with/eat/kill eachother, and you dont want that to happen