Isn't that sweet! I had one duckling hatch and roll a wrong pipper into the corner and sit ON TOP of the egg like it was trying to help. I went to work, came home 5 hours later (expecting to assist) and he had hatched! At about 43 hours from first pip.
Its close to midnight here, so I'm about to go to bed. Trust your gut if any of them look distressed, but as long as they are getting air, even if they are resting, I think your humidity is high enough for them to not get stuck. So "try" to let them do it on their own, unless you feel they can't.
Talk to them, even sing to them! It can actually help!