IMO all the symptoms your goldies are suffering from can be from lack of pristine water quality. I say pristine because these fish are well taken care of in asia, they aren't the run of the mill fish we treat them like. They are very well taken care of and treated with the upmost care, meaning very diligent frequent water changes. What a pain in the butt, right? who wants a fish that needs that much attention? Well... IMO, if I was doing a goldfish tank, i'd do just a few in a very large aquarium and put an autiomatic water change on the tank. This would consist of a tube of water filling the tank very slowly while a drain line slowly drained off the excess. If anyone's seen the old aquarium with africans at the airport, that's how they maintained it in between services for algae removal and debris removal. Grows fish quickly, and keeps finiky fish that can take your tap water's pH and KH looking happy.
Otherwise, I think you'll be fighting the renal failure (dropsy) until the end as well as the other skin infections. IMO, i think you're dealing with non-parasitic infections. anchor worms are obvious and easy to remove manually, ich is obvious and usually induced by some stressor or environmental factor (controlable by the aquarist), hexamita -well yeah that would help the hole int he head, but i think you've ID's your ailment incorrectly. A wen issue is usually an infection due to bacteria, and not a parasite. It could also be from physical shock to it's flesh where it was torn/eaten/removed. I dunno. IMO and experience, dosing for "just in case" is goin to wreak havvok on the fish's immune system and therefore cause more hard than good.
Med's are great when you're QT one fish and it's a for sure thing, but when it's not, it usually doesn't help the issue. Plus that med is probably depleating all the beneficial bacteria in your aquarium, making it harder and harder to maintain appropriate water quality for these finiky fishes.
Like i said, you've got your hands full