Don't put too much stock in my guess; I don't know much about hingebacks. It's just a guess from comparing the younger two to a photo from Vetter's Terralog 1. Good book if you haven't checked it out.
Looking at a range map, it seems unlikely to be K. b. n. anyway, if they are WC from SA.
I also feel these are speckii with a possible exception for the one in the middle unless they are all from the same batch of eggs. If the center one was from a different clutch is it possible to get a side pic of the beak and how many claws on front feet please? I'm very curious to be sure just what that one is.