A QT tanks is a great idea for wildcaught fish (which a lot of the different polypterid species are). But at this point, you should treat the whole tank they are in anyways, to be sure to eradicate this pest. When I had this issue I used the prazipro on my heavily planted 75 without issue. As long as you don't have any incredibly sensitive fish in the tank, and you dose properly you shouldn't have any issues.
You described seeing white blotches on your fish. This is most likely the secondary skin infection(hemorrhagic septicemia) that I was talking about, and is also a threat to your fish. Treat this with strong anitibacterial drugs. I have used sulfathiazole with success, and I also hear good things about furan 2. The reason that I like sulfa is because seachem makes a sulfathiazole product which is meant to be added to their food. If they are still eating, this is the best route to go. The reason being that the medication is going directly into their body as opposed to slowly being absorbed through the water column. I would also use the API sulfa tablets to treat the water, but the main medication would ideally be ingested. That being said, this infection does not necessarily come from the worms. Any external skin damage could lead to this issue (especially with ropefish). For this reason, it is probably not the best idea to house syndontis cats or most species of plecos with polys, especially in a smaller tank like yours. If they do cause damage to your polypterids, you may be fighting a constant battle with hemorrhagic septicemia.
I would stop using other medications for the time being such as paraguard, melafix, or pimafix as these will have no effect on either or your two issues. (but these products are worth their weight in gold in other situations) The best route to go until your prazipro arrives is to raise the salt level and the temperature and decrease the photoperiod.
Good luck!