It worked! Sort off...
the thing I didn't consider was that the new chicks don't know the routine. Buffy was terrific this morning. Her chicks were out of the nest as usual, but the newbies weren't for quite a while. Buffy kept getting back in and covering them.
Then, when all the chicks were out of the nest, she went out followed by her original brood. The 3 new chicks didn't know what to do and in the end, they huddled together against the wall. It was in the low 40s here and windy as could be. I finally went down to move them out to be with Buffy. She came charging in the moment she heard their protests!
Long story short -
I got them under her out in the covered run, and put out more of their food and water within reach. They are all hunkered down under the ramp. Going to go check on them periodically but I think that she will take care of them fine - I just need to make sure that everyone goes in this evening.
Thank you thank you thank you!