I have 11 week pullets and they just started sleeping on the roost last week. I actually have to set them on the roost every night, because they can't quite jump to it yet (it's kinda high). The first week or so that I had them in the coop, they huddled in the corner together, just like you described.
I'd give them a few more weeks. Just set them on the roost at night when you tuck them in. Don't worry, I'm sure they'll get "the hint".
I put the small cage I brooded the chicks in, in the coop with my 2 SLW hens. When time came to let them out, I left the cage in for their security. The silly birds still went back in their cage for weeks, then roosted on top of the cage, then finally rustled the "big girls" over for their share of the roost.
Mine did this too at that age and for MONTHS beyond actually. They slept in the corner of the run rain or shine, until the first snow fall, when they FINALLY figured out going inside the coop might be a good idea. Then for several weeks they would sleep on the floor of the coop in a pile. Gradually they figured out the roost concept and now a year later about half roost and the other half stay on the floor. Some are Silkies though, so roosting isn't so big with them. I figure, as long as they are happy, I don't care.