What breed are we talking about? Some breeds like Silkies don’t roost. Heavy breeds don’t roost high up an like a wooden board or a sturdy slat.
Roosts should not have sharp edges and if you use branches they should be quit thick
Can you post a few pictures? Give sizes?.
Give it time.
If possible make another roost away from the older hens. Its most likely they will all sleep in the same part of the coop after some time. Is it okay if they don’t?
I had trouble with bossy hens hens too when younger hens wanted to roost in the same area. Nothing helped really...