The best thing to do is block off the boxes, that's what I do when my hens are broody and resting on eggs. If your hens are sleeping in there you can block it off with plastic containers or plastic wiring secured on the top and bottom with heavy rocks.
You can take the hens or chicks and place them on the bars at night. I plan to do that with my mutt/ Bard Rock chicks and eventually they shall get the idea. Just keep trying to get them up there.