PrObLeM ChIlD,
Ich is a parasitic infestation so I would treat the entire tank to insure that it does not spread. If you remove the ones with obvious symptoms and treat them and the problem remains in the tank, you risk reinfecting them when you put them back in.
Often the first sign of the fish getting ich will be rubbing against the gravel or decorations in the tank. This is because the parasite is developing under the scales of the fish and is not yet visable. It is possible to have the problem in different stages of development from one fish to another in the same tank.
I suggest you raise the temperature to 80-82 degrees and put one rounded tablespoon of aquarium salt per 5 gals. of water. At the same time, use a commercial medication. And it is important to take the charcoal out of the filter until you have finished the treatment.
That is how I would treat ich. But now I want to question the diagnosis. You said the the fish with the white spots had these spots since she has been mature. How long has that been? Has the problem been getting worse or staying the same? If it is ich, I think you would see the problem getting worse. And about the neons; you described them as losing color. Are they fading or actually getting spots on them?
My concern is not so much that you treat them for ick if they don't have it, but rather that you might waste time and not treat them for something that they do have.
The following is a link to a description of the life cycle of ich. There are descriptions of other fish diseases at this site, too. I hope it is helpful to you.
http/homepages.tesco.net/~davyreynolds/f...hhealth/ich.htm