Two White Leghorns Not Laying

[silkie1472]

I have 6 white leghorns that range from 6-7 months. Four of them lay regularly, but they other two are not even laying. One of the hens that is not laying has layer two eggs that I am aware of, but that is it. The other hen has not even laid an egg yet. These two hens were slow to develop and I could understand why they might not lay as much yet, but the others are just fine. One of the hens got sick around the beginning of November and had a thick, yellow mucus come from its nose and was not very active, but now she is happy and healthy. Well, at least in my opinion. They squat when I reach to pick them up, and this was always an indicator of hens that are laying or approaching laying age, so do any of y'all have any idea of what could be going on? Here is a picture of all of them:

 

[silkie1472]

The hen that has not laid at all yet that was once sick is located to the left of the feeder. The hen that has only laid two eggs is located at the bottom of the picture closest to me. This picture is about four weeks old, and their combs are a bit larger now. If y'all have any questions or concerns about them, feel free to ask/tell me.