Hen sitting and hatching chicks

[Northumberland]

My clucking hen was sitting on 18 eggs, I know that's a lot, however the chicks are hatching, we have 8 chicks and only
5 eggs left, what could have happened to the other 5 eggs.

 

[Happy Chooks]

They probably got eaten by the broody, or broken when other hens tried to get in the nest.