If I were you, I would return the large fishes (the tangs and butterfly) back to LFS.
For the rest of the fishes (the puffer and the lion), prepare a trashcan to be used as hospital tank for the rest of fishes. The trashcan (a new 32G round) should be as dark color as possible to help calm fishes down. Add powerhead, heater, check salinity and ph. You do not need light for the hospital tank. Add 2 bags of charcoal into the trash can and change weekly. Monitor ammonia and nitrite in the hospital tank, and be prepare to change water as needed.
Medicate both tank for at least 6 weeks until you do not see the symptom on fishes PAST 6 weeks.
(scratch out the charcoal part, I forgot, they will absorb the medication, if you are using copper, render them useless)
By the way, you should consult with others to find out what kind of parasite your fishes are having, and get the right med for them.