For some reason whenever I get a stubborn one that is not eating... frozen krill always brings them right out of it. Being that they are newly aquired, I would give them a little more time. Also, you have to take into consideration where you purchased them from. The stress and trauma of being packed up and taken to a show where hundreds of people touch you and gawk at you.... also do you know where the person you bought them from got them? Were they WC or did he/she breed them?
If by this sunday they still have not eaten, Take them into your local vet (any vet can do this) and have them administer them a Vitamin B shot. Vitamin B will stimlate activity and appitite. It is possible that they were kept in a cold environment before the show and are slightly dormant or approaching a winter-state.
I would strongly suggest getting them in a bigger tank too. Two in a 20gal is not nearly as big as it needs to be. You need 10gals for ever inch and assuming each one is 4 inches you need an 80gallon aquarium. You and your turtles will be much happier.
Good luck.