Low in pecking order...won't lay eggs in nest boxes

I have a small flock of chickens that are just starting to lay...they are in a small coop. I have 3 nest boxes for 11 chickens and so far, so good with most of my chickens. I have three pullets that are younger than the other 8 and they co-habitate but the three younger ones are terrified of the older ones and spend most of the time up on the roosts while the older ones are down on the floor. I have water and feed for them up on top of the nest boxes and they will go up on those too. The youngest are starting to lay and I find all their eggs under the roosts. I think they are afraid to go over to get inside the nest boxes when the older ones are inside the coop. I put the older ones out in their tractor for most of the day, but read where I should keep them inside until they are done laying for the day, so it's been quite a bit later when they go out. The young ones don't have as much free time in the coop alone now. I'm in the process of building another tractor for the young ones, but until that happens does anyone have any suggestions? I wonder if it's okay to put a nest box right nest to the roosts? Or would that just turn into a bed for one of the higher hens?