I would assume (not having had a 6 month old BP with an RI myself) that the vet will treat appropriate to age, weight, etc. just like they would when treating an adult dog vs a puppy. Just make sure the vet you pick does have actual herp experience and then go from there. The snake needs to see a vet as soon as possible.

For now I'd put that snake on layers of plain white paper towel as a substrate (something I think is smart with any snake with any medical issues). I'd make sure the two snakes are in different rooms but consider both in full quarantine and watch that other one like a hawk for any signs it's also becoming ill.

Make sure you have gel hand sanitizer and do all your husbandry with the assumed healthy snake first, then anything you need to do with the sick one afterwards. After that wash well and sanitize and don't return to work with or handle your remaining healthy snake. You want to minimize any aspect of you being the transmission of germs between those snakes. Make sure they have all their own equipment and nothing is shared between them including equipment, prey, etc.