Candle and make a small air hole. Honestly at this point I would remove the egg at the air sac part and leave the rest that is at chick level. Then mist or oil the membrane to check for veins.
I say open the eggshell in case they look like they pipped but their beak is still below the membrane. You would want to gently tear/cut near their beak in that case.
(And for those hatching duck eggs, a beak showing isn't a yay they can breath sign. The membrane had to be taken away from the nostrils. Just had a duckling die because I thought it was breathing through it's mouth and it still managed to drown.)
Keep misting the membrane when checking on it but keep it in a high humidity incubator.
When the beak is out, take a small syringe, q tip or even your finger and get a drop of save a chick or similar and place it at end of beak. Give them electrolytes every once in awhile but don't do it a lot at once (say, 3 drops max.)
If it doesn't make an progress in 12-24 hours, then you can start making a crack in the egg in a straight line down so the chick can more easily push it's way out. Sometimes the eggshell just has more calcium than average.
