laying hen

Hi I am a newbie to chickens I have 3 hens and a rooster they are my pets and very tame.. My hens have been laying pretty reg for 3 weeks usually they lay and leave but 3 days ago one of my hens laid an egg and has not budged since. So I decided to let her have it but today there was another one. So I was wondering if I mark these 2 eggs and take the others when she is eating will it upset her and make her lose interest? Also is it 21 days or 28 days till the hatching? It also seems that my other girls have stopped laying should I move her and her eggs to a different spot? as I have stated I am a newbie but my chickens are very healthy and fed all the right things I keep them clean and fresh water everyday.