You need to isolate the sick ones from each other RIGHT NOW!
YES-- it can and will pass on to the others, if their immunity is down or they're predisposed to it, or had rough handling you don't know about before you got them! (You still have hope if you separate them. Never introduce new ones to an established tank until you have properly kept them separated for about 30 days to make sure they are healthy so you don't end up wiping out your whole tank. IF VISIBLY SICK: Pass on buying, but since you did, KEEP THEM SEPARATED, AND TREAT THEM). It's always better to buy from someone on here that is selling captive bred animals (CB) because they are healthier.
The best way to do this and cheapest I have found, is to either buy one of those "Critter Keeper" type containment systems, or get large Tupperware style containers at the $1.00 store and poke holes in the lids. Next, line the inside with some natural paper towel and really dampen one end and slightly dampen the other. Keep it slightly sloped so that the really damp end is at the bottom of the slope. This way they can choose their own dampness. Change the paper towel out every day. Use only dechlorinated water (per bottle directions) in the sprayer to dampen the towel with.
The best way to tell if it is fungus, bacterial, or viral is to take them to a vet that works with exotics. Call around. There might be one that will see your newts at a significantly lower price, and be just as good as another vet. ($34 vet bill vs. an $86 vet bill) There they can swab, run blood tests, etc. to determine what is going on under a microscope and actually prescribe something like Silvadene which has antifungal and antibacterial properties, or the appropriate antibiotic, or whatever they specifically need.
If you can't afford the vet, or their isn't one in your area, see my thread ("Help..I can see my newt's skull!!") for links for help. My best wishes to you! "Sick Newt Disease/ Parasite/ Fungus" is also a wonderful thread to look to for information.
Keep us posted please,
Critter Mom