Hatching eggs with mother hen

I have three broody hens right now and decided to give them some fertilized eggs. The hens have been great at sitting, but often swapping spots and sitting on top of each other to get the besting box with the most eggs. I candled the eggs at 8 days and 15 days and there was good development in all but 2, which I removed.

Today is day 21, and no hatching yet. I’m trying not to hover too much, but am beginning to wonder if any will hatch. They are in an outdoor coop and we are in a New England climate.

I’d love to hear other’s experiences hatching chicks with mother hens!