You are doing the best you can, and that is good. How awful to have this happen like this. I'd be chewing that breeder a new you-know-what, even if I decided to keep them.
I cannot stress to you enough you NEED to order Provent a mite. Mites reproduce faster than anything except maybe fleas. If you see them on your snake, I promise there are thousands that are too small to see yet. I spent 6 agonizing months eradicating a mite infestation. I treated and treated the tubs, rack, floors and snakes, and about every three weeks they'd start reappearing. I finally figured out they were getting behind the baseboards in the room where the rack sits, so I started treating there as well. I finally got rid of them, I haven't seen but one in the last four months, but I still treat preventatively once a month.
The RI will for sure need vet care. Don't fool yourself into thinking otherwise. The hardest part will be the shots, so make sure you have the vet teach you how to give them. Keep them warm and make sure you empty and bleach the water bowls daily to prevent them from re-catching the germs. It helps to have two sets of bowls, that way one can get a bleach water soak and you can put the clean ones in with the snakes.
Snakes with mites do soak a lot, so that is why they are dashing for the water bowls. It may help to only cover the bottom of the bowl with water, since you'll be changing them daily anyway. It means less to spill when they try to soak.
I wish you all the best with whatever you decide to do.
Gale