I have the same question Amy asked -- how can you tell they still have yolk?
If you can hear them peeping, then they are most likely internally pipped, meaning it has broken into the air cell. And if one pipped on day 23 and hasn't hatched by day 26, I would assume it quit.
Can you get some pictures? I'm thinking your terminology may be a little different than what we are used to, and maybe I'm just not following you.
Also -- not being mean, because it happens quite often, but are you positive of the day count? What day did you set the eggs?
Duck crests are similar to silkies vaults, but mating them usually results in very low hatchability and/or neurological issues. Crested ducks in general usually do fine, if only one parent was crested, but can have issues. My Opie is still alive and well, he turned 2 a few weeks ago.