Thanks for all the advice. They survived the night and seem happy, spreading their wings... And it got colder than expected at 37°F. I noticed a non-family cat lurking around last night but it must've given up.
We have 4 NH Reds and 4 RI Reds in our brooder inside. We think they may be 3-4 weeks old, not sure. They are flying out of the 18" tall brooder and they like to roost on the feeder. Nights are in the low 40s now, would it be OK to put them in the outside coop if we move the lamp out too?