It's very hard to judge by just a picture or two. I wouldn't sell your partridge just yet. It may have the best type of the four. I would say your paint is very likely a boy. I won't guess on the others. I wouldn't worry too much about size at this age. In my experience small ones usually catch up. I think your biggest problem is wings. They all appear to have loose wings or split wings, but they are young and may out grow that. In my limited experience they don't. Split wing is a DQ. You mentioned they had been in the mud so possibly their wings are muddy and heavy or they are molting to a new stage. As far as keeping them, it depends on your plans for the future. Your partridge color looks normal to me but could be dark blue. Hope you get some other feed back!!