Rats don't get fleas, but they do get mites. Mites can be treated with a 1.87% Ivermectin horse dewormer found at feed stores. Make sure it only contains Ivermectin, and nothing else like selemectin or anything. It will cost around $6 for a big tube of the stuff. Treat the rats with a grain of rice dosage every day for 2-3 weeks. This will completely get rid of the mites and any other internal/external parasites.

The mites pose no harm to your snake as they are Tropical rat mites, and only infest rodents.

You may want to check on your husbandry. Mites come from dirty conditions and bad sources of bedding. You will want to freeze your bedding since the mites can live in that and may have come from the pet store or wherever you buy your bedding.

Just treat the rats and no one will get scabbies or skin infections. Hope everyone does ok.