I know there is a disease specific to discus that causes some of the symptoms you are describing, although the clearest symptom which I do not know if your fish have, is they turn almost a black color. The ich on your fish is probably just opportunistic, the fish were already weak. Although, I cannot remember the specific name of the disease, I do remember the treatment was to lower the pH over a period of a couple of days to as low as 4.5. After the fish have recovered, you raise pH back to normal levels more gradually for about a week. This information was from an article in Aquarium Fish Magazine by Jack Whatley. If you can find this article and the disease matches your symptoms, you might give it a try. I also seem to remember the usual passage of the disease was from new discus which you had. If this fails, Jack Whatley is supposedly one of the premier discus breeders in the country so you might try him for new stock.