The snakes with mites...are they quarrantined? If not...(quite frankly even if they are) you should treat ALL of your snake enclosures for mites. Including the rack that is holding the tub. Mites can get everywhere...you can have them on your clothes and then carry them to the other snakes.
I would recommend taking out the tubs...washing in a bleach/dawn/water solution. Rinsing and drying well, then spray down with Pam. Be sure to spray the outiside and the lip of the bin as well. Let it completely dry prior to putting the snake in. I would also at this time wash down the rack.
Then repeat this in two weeks. Personally I would do this every 2 weeks for at least 6-8 weeks. This way you can ensure that you are killing the mites AND the eggs.
Also be sure after you treat everything that you wash your clothes and take a shower prior to handling any other reptiles (lizards etc.)
Now this could be a little overkill...but I am fairly anal when it comes to making sure you get it all and get all quick. We recently were taking care 42 reptiles in our house (a friends stuff). One came in with mites....even though we checked prior to it. I used this technique on eveything and we have NO mites thank goodness...my reptiles were never affected so we were able to squash the situation quickly. ....whew...
Just remember...mites go everywhere and love to lay eggs in corners and tight areas...nasty little things