Use the Blu-Kote once or twice a day for 5 days, throw some Tnactin into their dust bath, and see how it goes. If it spreads, they may need seen by a vet, but generally fungus can be handled very easily at home.
You will need to make sure the cage is entirely cleaned - either throw away or boil and bake any wood items, wash the hammocks and so on in hot water and dry on high. If you're in a sunny area and can do it, drag the cage outside and let the heat beat on it for a while.
BTW - Don't assume that fungus will spread just because they are in the same cage. Fungus generally happens because of a breakdown in the immune system of the chin that has it, especially if there has been no outside exposure and you have good husbandry. Fungus can literally pop up just because of a lowered immune system and stress.