They lay during the day so where they sleep shouldn't have much effect. Lots of folks have community nest boxes. Some hens do seem to prefer a more private nest box, though. Or at least a somewhat darkened one. I think there is an instinct to lay in a hidden spot, to keep predators from getting the eggs. I imagine the strength of that instinct varies from bird to bird, though.
I'd certainly do what I could to stop the nest sleeping, though, or you will get poopy eggs. If they were younger I'd suggest closing off the nest boxes til they get older, and put them on the roost each night just after dark til they go there on their own. You may want to do this anyway.
I've never had to teach chickens to sleep on the roost. You might check out the coops section or make a thread to see if you can figure out why they sleep in a nest. Or, just tell us more about your setup and what the roost is like.
I don't believe that the lack of privacy is why they aren't laying yet, though. When they are ready, they will lay. If the nest box is closed off when that happens, you will find the egg somewhere else.
