hatching eggs 24 hours behind the others

Hello, I'm new and I've tried to find advice, but I'm not having much luck as there's so much info on here I had 6 eggs under a broody hen, 4 hatched yesterday morning, today is day 21 and the other 2 are showing no signs of emerging. I candled them all a week ago and they all had contents.
What do I do? She's been out a few times today rosey, I guess trying to get yesterdays hatched chicks out, but she returns to sit on them and the other 2 eggs. They all went under her on the same day. I have read that some take longer to hatch, but I also have read somewhere that usually the cheeping of one or two makes the others hatch?? 
If she leaves the nest with the hatched chicks, do I open the other eggs? Or try and incubate them (I don't have an incubator, but I do have another broody I'm trying to break!) Any advise greatfully received! 

Ha, joyful-fastfingers beat me to it!