Is it possible to get at least a 20-gallon for them? I’d just worry managing water quality with two tangs in a 5-gallon tank with medications is going to be extremely difficult...
Personally, I would do the rally bath. With infection already a possibility, it will help slow it down while you take care of the flukes first. While it is possible to mix antibiotics with prazi... it’s not ideal. And triple sulfa is a good antibiotic, but a little harder on the bio-filter.
If you did need to add antibiotics before the prazi treatment is completed, I’d agree with
@4FordFamily that the trifecta (kanaplex, metroplex, furan-2) is a safer bet.