Multiple Budgie Eggs Hatching At Once?

Hello, I have a pair of breeding budgies. It is their first time I bred with them. They have seven eggs, the first one was laid on the 17/10/18. Then three chicks hatched 7/11/18 this morning. When I checked on the chicks again this afternoon they were all alive and fed. I don't know if the parents helped the chicks out of the eggs or what happened. The parents (mainly the male) is more protective then he used to be. When I checked on the chicks the male would try to sit on them, he has never done that before (maybe he is being more protective because of the chicks). I was wondering why they all would hatch on one day? Thanks.