It looks like it might be a case of scale rot. A trip to the vet might not be a bad idea. You said you just got these three guys today, where did you get them from? Do you have any idea of the conditions they were kept in? For the time being, i would switch over to a paper towel or newspaper substrate and change it out whenever it gets wet. Scale rot is definitely treatable and does disappear with a couple of sheds, but it is important that you dont allow him/her to lay in a wet substrate. If it were me, i would see what a vet has to say.