Why aren't My Hens Sitting on their Eggs?

Last Year of Spring,I ordered 6 hens and 2 Roosters. Well one Rooster, I separated from the other. Because I was going to Show Him. Well The main Rooster that is with his Ladies has been doing his job. I have a Hen house in my pen. why aren't they sitting on them??? I have given them Oyster shells, Scratch Feed( Everyday), and Laying Mash( Everyday). Please Help!!! Also, their Rode Island Reds!!!