Trying different things to make the nest boxes as attractive to them as possible will pay off. I had an issue like this for a while and then I noticed that because my boxes where across from a southern sun facing window, hens didn't like the sun in their faces. I moved them to the wall under the window and all of sudden they all used them. Also, I added a bar under the boxes to help them jump up and down. It's hard to tell for sure but your boxes look kind of high up on the wall, possibly. And the small one looks like not enough head room. Maybe add a different box type. It's truly about thinking like a chicken = I want an easy, comfortable way to hide from the rest of these bitches, while I lay my eggs in a place that I can hide them from the world.... 
