They've probably just got a cold, maybe even caught it off you
Pigs are very suseptable to human lurgies. Check their temperatures to be sure its nothing more, make sure they are warm (feel in their armpits to check) and so long as they are eating and doing all the things pigs do they'll be fine in a couple of days. We have an old geriatric pig who is continually snotty thro winter and he gets 10ml of calpol, which seems to help and the vet thinks is incredibly funny
also could be an allergy, have you changed straw or anything in their environment?
If it is snuffling it can be something called Atrophic Rhinitis, symptoms include sneezing, runny eyes, discharges from the nose sometimes containing blood and early signs of distortion of the face, with shortening or twisting of the upper jaw becoming evident at weaning time. It is important also to appreciate that sneezing is a common occurrence in the sucking pig and need not necessarily be associated with it. Caused by pasturella bacteria. Will normally clear up itself but can be treated with antibiotics if persistant.
HTH
mandy