September's Doncaster show? If you didn't take the seller's details I guess you'll never know how they were raised. There's at least two types of frog breeder, the reputable one who pays close attention to bloodlines, nutrition and providing everything a growing animal needs, and the bedroom breeder who kept two sibling frogs together and got lucky and managed to sell a few malnourished offspring and make a few quid. I fear you may have bought from the latter.
The damage has obviously been done before you owned them, but the best you can try is to pull the remaining ones around with a healthy diet of vitamin and calcium dusted crickets and locusts and of course adequate UVB exposure. Clean treated tap water changed every day, temps of 23-24C at night and 26-27C during the day and around 60% humidity. Splitting them up is a good idea as they are remorseless bullies. Good luck!