How old are they? Sometimes it takes them a while to get the hang of roosting. I have a batch of 8 week olds that still sleep in a pile on the floor all snuggled up with each other. It may also be a dominance thing if they are in with older birds who don't want them on the roost.
I have 2 standard sized cochins, 2 silkies and 1 barnevelder that are all about 7 months old. They have taken to sleeping in a pile in the corner of my coop instead of roosting with the older birds and they have done this for several months. I haven't really bothered to move them, though maybe I should. It started as a dominance thing. They were 3-4 months old when I turned them loose with the flock and they got slightly bullied, but nothing worrying. They quickly found there place in the pecking order, which was at the very bottom, and they have stayed there, not wanting to challenge the bigger birds. Now I think it's just a habit. They don't get bullied anymore. The other birds allow them to eat and roam with them without any troubles, but the little guys are so used to sleeping on the floor I guess it hasn't occurred to them to get on to the roost. lol So, I guess I'll start moving them into the lower roost at night and see if they get the message.
You guys think you had/ have a problem. When I had chickens, I had two and I had a roost but they NEVER roosted. They always slept OUTSIDE in the rain, cold, and near predators. They weren't very bright. Some nights I had to go out in the rain and LOCK them in the coop. Not the brightest animals but I loved them.
We have three that use the 4 ft long roost... three that sleep on the nesting box... and two that sleep on the floor in separate corners. Lol My New Jersey Giant has never roosted...EVER. She just doesn't like it. I haven't noticed anyone else being mean to her, and we've tried different heights... I just don't think she likes it.
My 12 week old chicks just starting roosting about a week ago. My smallest one still can't get up on the roost by herself, so I set her on there every night. The absolute cute thing is, a couple of the other girls will actually either get down from the roost or move to the lower one and sit as close to where she is on the floor until I get her up there. Then they move up too.