Sneasing is normal. Ferrets are constantly smelling because of there poor eye sight. So as long as they are healthy looking otherwise, eg. not having runny eyes, eating well, drinking...
They are fine.
But if they are acting funny and sneasing they might have a cold, and that warrants a vet check ASAP.
Some pet shavings have a high dust count and this could be causing your ferret too sneeze i recommend a type of bedding called Megazorb which is like crumpled up bits of paper. its a little hard to explain but im sure if you google it you should get some pictures of what i mean