I can;t help with the chicken eggs, but I can tell you a little about ducks...
Humidity is extremely important to the hatch process. if too low for too long the membrane inside the egg is like leather and the duckling cannot break thru it. The conditions during the 28 day wait are very important and its easy after a few tries to see and know whats going on. I candled almost everyday to watch the growth and see the development and to learn about what to look for. The size and shape of the air sack is important and tells you how healthy the egg is. Drowning in the eggs takes being underwater almost....its a LOT easier to be too dry. Many folks use a plant mister spray bottle each day to wet the shell besides any water container that's in the 'bator. I'd rather have a duckling that's got a soft membrane than one that has to have a chain saw to cut thru ....The shrink-wrap can be fatal as the duckling gets exhausted trying to tear thru the plastic like membrane that's just too tough and they die before getting their head out. Once they pip, they are on the clock. Times limited.
This gets very tricky since this is when you need to make a judgment call. To help or not.
IF you decide to help and I use a min of 18 hrs of little or no progress as a guide, then it has to be done with great patience and a delicate touch.
get a dental pick and look closely at the egg where the duckling has its beak. The first thing out should be the beak so it can breath,,,next the head. Pick away small, TINY flakes of shell to help free the beak and head. The membrane will still be around the duckling and hopefully it will be able to tear thru that. That's the hard part because the membrane is still full of blood and if you tear it in the wrong way it can bleed out....
IF you do have to cut membrane do so slowly and wait. Cut until you see ANY bleeding and stop and wait for that to end and dry out...several hours usually. As that portion of the membrane dries you can cut more in a slightly different area (to give more time to dry where you previously cut) and chip away more shell. Once the beak and head pop out you;ve pretty much got it made,.
When the whole bird emerges, do NOT do anything at that point...the duckling will still be attached to the membrane sack by the cord which you do NOT CUT>...let that dry on its own and it will break away after a few hours. The duckling will struggle and be weak but that's part of the process. Provide shallow water and allow the ducklings to dry out on their own. Keep them warm at around hatch temp of 99 degrees. After the hatch I used a heating pad under a container to be the brooder-box where they stayed warm and on soft bedding. If the duckling is too weak to get to the water....I use an eye dropper to place a single drop on its beak. It will open its mouth and allow the moisture to enter. If it does, add another drop until it does not open anymore. The first meal can be hard boiled eggs...mashed to a mushy consistency. Ducklings are able to eat solid food from day one but I like to start off gently and give them what they are familiar with....egg protein.
The trick to helping a hatch is not to get in too big of a hurry. It takes 24 to 48 hrs sometimes. If the humidity or temps were not perfect then it does have an effect but its not disastrous. All you have to do is go slow and most important of all, be patient and do not cause bleeding of any sort...just pick away a little bit, cut a little bit and wait. Its like painting the wall and after each brush stroke you wait for that to dry before you can paint the next stroke....slow and tedious.
There are few things that bring more joy than watching life begin....it can be as exhausting for you as it is for the ducklings but worth every minute of work.
have fun!
