I have had this problem too, recently. We got 2 new pullets and our original pullet, Batman, has been kind of bullying the newbies so they can't sleep on the roosts but rather they hide out in the nesting boxes. They're just starting to lay, so I've opened up access recently to the nesting boxes (they were closed off before when they were younger). I've found that it's easier at night to scoot them out of the nesting boxes and onto the roosts. Sometimes I have to go out a couple times, but I'm hoping it will catch on in a few days.