After many delays about getting a heat lamp in the coop, I finally decided to just leave the 7 week old chicks in there overnight last night, with no heat, no light. I thought it would only get down to 46, but the thermometer said 40 when I got up. They seemed fine when I went out to feed them and the big girls. Catjac, your plan helped me be determined to just leave the girls out, and know they would be ok.
They are not as tame and docile as I wanted by this time. Roger Rooster is very skittish, and I think the girls follow his lead. It may be that I didn't spend as much time with them as I did my first flock, two years ago. The older girls are really skittish and cranky now too, as they are all in some stage of molt. It looks like a chicken massacre around here.