So I just attempted to candle the eggs with a torch; mumma was very patient with me. I could definitley see the air sac and an area that was dark, no movement however or chirping. It has just started pouring with rain so I may check again tomorrow? Chick is still happy under mum.
You do need to make sure the one hatched chick is getting to eat and drink.
The reason to candle the eggs, is to know if all of the other eggs are empty of have dead chicks in them. If no other eggs are going to hatch you can remove the eggs so the hen can mother the chick properly and make sure it gets to eat and drink.