Opened the one we thought was dead, and yes, it had died, was fully formed and had absorbed all it's yolk etc. Opened the one we thought was alive, and it was alive, but not very well. Very little movement and hardly breathing. Had also absorbed yolk sac but still had a few veins. It died not long after opening, but I think it was going to die regardless of what we did. There was very little movement from within the egg even before we cracked it.
After doing some research I'm pretty sure they had both picked up an infection from out chooks. Three out of 8 of our chooks were laying beside her dispite our best efforts to encourage them to lay in the new box. I didn't realise there was any risk as it was our first time with ducks and definately out first time with natural incubation. A few weeks into incubation a chook egg got broken spilling contents onto two of the ducks eggs. I cleaned up the mess but again was unaware of any risk. Anyway, lesson learnt, and will make sure it doesn't happen she decides to hatch more ducklings in the future.
On a brigher note, her and her 4 ducklings are doing really well and she took them for their first wander today. Tried to introduce Bob, the drake, to them but all he was interested in was mounting Pip, so I removed in from her sectioned off area.