I have a better solution. I have extensive experience in this field and what we got to do is give your fish a chance to recover.
Flukes do not kill the host but the complications caused by their existence on the host is (Wounds get infected etc.) RFH refers to it on calcareous corals but this seems to apply to trematodes etc as well see
Phosphate and the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com
To raise it I use Activate from Aquavitro. only a drop or so is needed - depending water volume.
Praziquantel is the correct route but judging by the advanced stages I would raise the Phosphate levels in the tank.
You probably would wonder why ? Elevated levels of phosphates in water 0.1 ppm and (preferable 0.2ppm - 0.3ppm) stunts the growth most organisms - in this case flukes.
The other chemo theraputant is Copper but it comes with many other complications.
I have tested it with great success and it puts far less stress on the fish considering the other factors.
After they have recovered at these elevated levels, Then introduce an obligate predator like a cleaner wrasse.
Gradually lower the phosphate levels whilst delivering medicated foods with Maxilint in it and control the infestation like that. After a prolonged period you would be able to successfully eliminate the parasite. By treatment and predation.
As an experiment I have kept fish alive for over a year in elevated phosphate levels whilst infected with this pathogen.
I hope this helps
