We all know how difficult it is to identify the sex of these fish, so please post a picture in here and we'll try to help you (or at least give an educated guess!).
Looking at your pictures of the two zebras I would say that they are both males due to the fairly pronounced odontode growth. They also appear to be fairly slim in the mid rift area, again this points to them being males. With any luck the one in hiding will be a female.
If you could possibly take some clearer pictures it would be a great help. Try taking some over head and side profile shots of each fish.