Tesa,
Your chicks are too young to roost. They huddle together because that's the way they sleep under their mother's wings, and their feathers aren't developed to the point where they can fly up to a roost. If they were afraid (predators) they would try to get up as high as they could, which may be why they are on top of the box. Try putting a blanket or tarp over the exposed sides, just for the night.
You'll need a bigger coop as they become adults. 4'x4' isn't enough space for three hens.
If you think they cheep now, wait until they are adult and carry on constant conversations! They gurgle and tsk-tsk-tsk and celebrate out loud after laying an egg. The noise is worth the delicious eggs, though!

i was thinkin' of buying a smallish tarp just for that.

i've seen them fly up to the roost, but during the day

their run 10ft x 4 1/2ft, and i intent to allow
them free range of our 1/2 acre, but not for awhile, as
they are still small, and i want to be sure they come home
to roost at night

the way husband built the "platform" the kennel is on, he can frame it all in, and they'll gain about 2ft all the way around, so it will sort of morph into a 6ftx6ft coop
once that happens, next paycheck

can't wait to hear more of their voices, a friend has a
few, and i love to listen to them as they go about their days

thanks

tesa