hmm. I'm no expert on shrimp, i've only had a couple and they both died trying to shed. I know they're sensitive to most medications, especially ones containing copper. like snails. but i think shrimp are more delicate.
because both shrimp and snails are unlikely to host the parasite maybe you could quarantine ur betta and treat it separately. u'd still need to change water in the main tank and vacuum gravel really really good. i'd also still increase temp and add a bit of salt in there, but maybe someone else could advise you on proper dosage because i can't vouch for what shrimp can handle. Unlesssss!.. you don't have many shrimp and you can just quarantine them and snails and treat the fish in the main tank. That would be better i imagine.
Kordon Ich attack is supposed to be safe for everything, but to my tank it did absolutely nothing. but some people swear by it.
Metronidazole is what helped me, but it could affect your shrimp if you just doze the water. However, if you also get a food sealant you could just feed the fish medicated food (and that's supposed to me more effective anyways). so you could try that.
as far as treating just the fish, you can pick between heat and meds
i hope someone who's more educated on shrimp will respond though