Looks to me like you have a pair there, but I would have to see better pictures of each duck. You will most likely be able to tell at this point by the sound of their voices. Ducks mature pretty quickly. Sometimes even quicker than chickens!
The two you want to breed look to be pretty nice. They aren't quite show quality, but I'm sure you could work up to that! Personally, I just like to breed things and see what I get. If that's all you want to do, than go for it! I have yet to try and hatch ducks, but I would love to give it a shot this spring.
Good luck with your duck breeding! I would love to try runners, but it's so difficult to find anything around here!