My first hatch was going smoothly. Multiple questions?

[Creadh]

I have a broody white cochin that I decided to let sit on eggs 20-21 days ago and this morning she hatched three perfectly healthy chicks and one chick who still had the yolk attached to its stomach. The chick that has the yolk attached to it is going to die I think? It got all sticky and has been laying there for about 5 hours. It is still breathing. Another egg pipped about an hour ago. There are two light brown eggs left under her and I candled them with a flash light. the air cell is large but I can't tell if theres a chick inside on either one. Should I leave them for a few days or toss them? I also jumped at an opportunity and I put three 1 day old ducklings and 2, 1 day old australorps in front of her. She took them almost before I could set them down.