Late last night/early this AM other hen hatched out 3 of the 6 eggs under her. Like a dope I didn't think to mark the 2 eggs I gave her from the other hen's nest until too late, she had already tucked them in among her other eggs and I couldn't tell the difference. So I don't know if any of these 3 had been under the other hen for the first 20 days.
I found one chick in its egg with much of the shell gone but the membrane mostly intact, and gone dry & tough. I carefully snipped through it with scissors, wet it with water, and put it under the hen. A few hours later it was still in a half-shell, like an oyster, when I pried the shell loose the chick came free.
This AM that chick was dry, fluffy, & doing fine but I found another chick, damp & newly hatched, laying in the straw a few inches from the hen. It was still alive, but cold. I put it back under the hen and it too was fine, dry & fluffy when I checked on it this afternoon.
There are still 3 eggs under the hen, if they haven't hatched by morning I'll have to bury them. In total there now are 5 hens with 23 chicks, and still another hen setting on 4 eggs behind the duck house.