Filling the shell is a good sign. Leave them be and just wait. Sometimes they can take a long time to hatch. Never had duck eggs, but if they are like chickens, patience is a virtue with them. Not familiar with that breed, but I think some take up to 32 days to hatch.
Have you candled them? When was that? For now, like chicken eggs, I would assume to leave them in there a few more days just in case. What kinds of ducks are these?