A few things come to mind....... maybe the house is too big for them and it's getting chilly in there,so they go for the places in which they stay warmer. Solution; get more chickens!!! Or they haven't bonded yet as a group yet and the cock is herding them sufficiently enough. Solution; give it a few more weeks. (more likely) Or,maybe replace the perches with a bit of real tree,something a bit more natural.
Mine did exactly the same for the first couple of weeks. I can't tell you how much trouble I went to adapting a slice of the barn for them..... solar lighting,nesting boxes from a wardrobe turned on it's side,roosting perches et al,and they ended up roosting on top of the wardrobe of a night time. I put a dead branch from a pear tree in there and they seem to have taken to it.
Doesn't sound like you're doing anything wrong,(never work with children and animals),maybe someone with a bit more experience will post an "all-knowing" answer and quick fix solution,but my guess would be,just give it time..... Ree