How exactly do their faces look like? Did you notice anything else anywhere on their bodies, such as gray films or some cottony growths, etc ... ? The disease seems very contagious. Do you have a separate tank where you could quarantine the sick fish (in order to prevent the spread of the disease to the rest of the fish in your tank)?
Read the "
freshwater fish diseases" section on Fish Lore and see if any symptoms match those described there so that we could determine exactly what disease your fish have and to see what the best treatment is.
At this point, if you're uncertain what disease it is, the best thing to do is to perform a larger
water change (30-50%). Water changes are always a good idea when fish are sick. Another natural treatment is aquarium salt. There are varying opinions on how to use aquarium salt. However adding 1 tablespoon of aquarium salt per 5 gallons of water is safe. Another way to use salt as treatment is this:
http://www.fishlore.com/Forum/index.php?topic=1111.0