I'm not really sure the best method to treat rats for mites, especially because there are babies too.
I found this site: http://www.fancypetrats.com/pet-rats...ites-fleas.php
But I would call your vet and ask before doing anything. Seems like its relatively simple. Also be sure to let your vet know they are destined to be food and find out when or if it will be safe for the snakes to consume them after treatment.
Good luck and hope they do ok.