Well, considering what they have been through, they don't look terrible in the pics. A vet visit is the way to go. I would separate them immediately. Could be a lifetime of domination that has caused the difference in size. I got 3 last year that had been kept together and 2 of the 3 were skinny and small. Since being separated they have thrived. Regardless of what you paid, you should be commended for taking care of them!