Have you had any luck in breeding them yet? I know you said you didn't know who was who as of now. I didn't know with mine untill one finaly kept hanging around with another one in the same shell. Finaly the male got big enough to where it was fairly simple to tell them apart.
They are quite interesting shellies. I've got a m&f in my 45 gallon right now and am expecting a spawn anytime. Once they do I will be adding another female that has previously breed with my male. Mine were sold as 'Katabe', but I've always tended to lean more twords 'Mtoto'. Like it matters, they are great.
If I were to venture a guess, I would say that in the first picture the one on the right is a male, and the second one is a male. The reason I say this is due to the facial profile. IME the males have a more elongated face and I guess because of that the mouth and eyes tend to look larger as well. Just what I have noticed, YMMV.
BTW-I love the 'aged' lood of the shells. Adds a lot to the photos.