Best thing to do at this point is let them settle 24 hours & then set in a carton in the bator without turning for another 3 days. Check air cells again on day 3 to see if they are more stable. If not, leave in cartons & just tip the carton. If they look like they have reattached they can be laid down & turned by hand or in the turner.
The reason they took so long is because your temps are WAAAAYYYYYY low. Probably why you also only hatched a few. Temps should be 99.5 for a bator with a fan & 100.5 for still air. Even temps to 101 are ok. Below 99 will delay hatch by a good bit. You probably also drowned several with humidity so high. 40-50% for incubation in still air, 50-60% for lockdown. Add 10-15% for forced air to each of those humidities.
Not sure where you are located but could be that ambient temps were low while the hen was sitting on them which would also delay hatch. If the eggs got too cold for too long it would kill them. Low temps once they warmed back up would also delay hatch & humidity too high can also kill anything not yet hatched because they won't lose enough weight to be able to turn to pip.
So when they say that call ducks are hard to hatch, do they mean the incubation process of the growing embryo or the ducklings actually hatching out of their shell or both?
