Couple of things:
1. Were these captive bred or wild caught? If wild caught, then you could also be dealing with parasites along with the potential URI.
2. You should see a herp vet if you are having problems. They could do a fecal exam to check for parasite load, a review of their blood to see if they have any elevated levels signaling some infection, etc.
3. Did the seller provide any guarantee? How about follow-up husbandry info? This is the responsibility of a good breeder and the difference in price from a imported/farmed animal.
4. Search this site and VPI.com and NERD for caresheets to verify that you cage setup is correct. Respiratory infections develop typically when then are subjected to suboptimal temps and also to poor air flow. Also, wheezing type noises are not always a sign of resp. infection, it could also be from them hissing at you. Too much humidity is bad (ie damp, limited airflow), but even amount is necessary for proper sheds.
If you need help finding a vet try www.arav.org
Good luck.
Rich