Can you give the male with the fungus on the tail a salt bath? It could be at a marine concentration or even higher? You put him in there until the fungus drops off or he shows stress and needs to be removed back to his tank.
(You may need to buy a "cheap" hydrometer. Get the floating one with the thermometer for convenience if you can. Later it will be very useful in hatching baby brine shrimp.)

Fungus grows where there is dead flesh. In a way fungus is a way nature cleans up.

Hopefully the fungus can be separated from the fish. You mention that you are medicating. What are you using?

You are facing the same dilemma as Maggie. The tail rot/ fin rot is often a bacterial thing, partly a result of dirty water. It could also be Columnaris. Do a 20-25% daily if you have the seasoned water of the same or slightly higher temperature. Add it through a very slow siphon. An airline might work best.

Administer an anti-biotic. It may work with either the bacterial infection or with the Columnaris.

When the tail rot is stopped, change out as much water as you safely can and administer either a straight anthelminitic or a commercial anti-worming medication. Not that it's right, but please consider my response to Maggie's dairy just below this diary.

The reason this seems like "The Curse of GL" is you now have an idea what is happening. The problems would happen anyway. You just would have less idea why.

(I'm listening to a radio talk show with all these experts while responding to your dairy. I'm really bothered by what has happened. But I'm even more alarmed that the U.S. may be in the gravest danger it has been in in 60 years. Knowledge can be a curse if one wants to be blissfully unaware.... at least for a time.)

As to the name game, squack you have signed posts "Scott D". So have I.

LOL
Please tell me that your last name isn't Davis. :)