So sorry you have had troubles. A first hatch is always nicer when its trouble free. You can use a misting bottle to keep the membrane wet- use warm water in it - rather than cold so you dont chill the duckling too much each time you spray. I hope the little one pulls through for you. If...
It could be that your temperature was low- That can increase the time they need from the normal 28 days - Or just that there is something else wrong stopping them from hatching since 2 are still alive. Being the wrong way in the egg- low humidity causing shrink wrapping by the membrane- or just...