There is a lot to feel terrible for here. The fish looks as if he likely has not been taken care of whatsoever. Small, pale, and huge eyes indicating likely stunting etc. With 3 standard goldfish, the tank would need to be fairly large too. Most try to keep these in small tanks. These regular goldfish are often insanely hardy and can live many years with absolute horrid treatment. This poor guy was found dying in a filthy tank. Unfortunately, the fish is a living thing too and deserves decent care and a clean home. It is not my place, but I would be the one to step in and gently educate them on fishkeeping and care. Direct them to this site or other resources if you can. It may help them along.