The only way you'll be sure is by taking them to an exotics vet. All guinea pigs sneeze from time to time. However, if they are ill, clearly it's important to get it sorted. One of my pigs, Heidi, came from a home that never took her to the vet. She developed weak lungs and now has plumonary fibrosis (lung scarring) because she had so many URIs. Her lungs are constantly 'crackling' now though she has no other symptoms as of yet. In the future her breathing will likely become more difficult and I doubt she'll live just as long as she could have had she been properly taken care of as a pup.
Obviously, as you've said, you don't want this to happen to your pigs.
I searched your ZIP and came up with this page:
VetUSA: Veterinary Listings for Louisiana - VetWorld Companies
Forgive me if it's not quite right; I don't live in the USA.
Good luck!