Nervous 1st timer here!

[arcountrychick]

This is my first time to hatch. Today is Day 20, but I've had 9 bantam cochins and 2 wyandottes hatch already. The remaining wyandotte eggs haven't even pipped yet. Should they have pipped by now? Also, all but 3 of the cochins still had the yolk sac attached. One didn't make it, two are isolated but doing fine. The others dried up and they are just fine. Did I do something to cause this?

I'm probably just overanalyzing this, but any advice is welcome and appreciated!

 

[Sphinx]

Sit on your hands for the final egg. I wouldn't start really worrying until the end of the 21st day. It sounds like things are going pretty well.