What occurs not so seldom, may be the mom is too tired to open the sack, / bite off the cord. So it is good to be there and be prepared to step in and help. You can use your own nails, moms teeths arent sterile.
Some forumists told the kitten get stuck halfways out. If you want to help, the trick is to carefully wiggle it out, trying to draw simultaneously as the mom is pushing.
Find a vet who is willing to give telephone guidance, and have the vets telephone at hand. OR some experienced breeder or rescuer. Even a such one of dogs may be helpful...
Kittens getting water in lungs...is a story by itself. Yes, it is a real danger.
Im in a little hurry, so I dont descirbe the remedies as now. But you got to try and get the water out, otherwise they usually get pneumonia, usually deadly for them at this age.
Weak, or seemingly stillborne kitten, sometimes perks up if you warm it up, with massaging as extra. Having a weak kitten on your breast beneath your clothes is a excellent help.
Yes, I had to break the sacks and tie off their little cords for Mommy when my six were born. Mommy was just too weak. They all were born healthy and Mom came around to clean take care of them just fine.