Temporarily Separating Brood Mates?

Hi! We have a flock outdoors of 8 currently (5 quailed d’Anver, 3 Welsummer) and have 10 total in our brooder (6 Barred Rock, 2 Cream Legbar, 2 Mottled Houdan). All purchased within a week of each other from various stores (BR were all one lot, Legbar and Houdan were purchased together 6 days later). The BR and Legbar are 100% fully feathered and ready to start to integration process to our coop, but the Houdan are much smaller. They appear to be fully feathered but their size difference concerns me. I know they are a smaller breed than the other two, but would this much variation be of concern? Or would there not be many integration issues with their current brood mates if we kept them indoors another week while integrating their mates?

Coldest upcoming night is 45 degrees, average high 50’s though for other days. the area inside the coop we have isolated with hardware cloth is large enough to add a supplemental heat plate for a few nights if needed for the Houdan’s should they be able to go out with the rest of their mates.

thank you all in advance, I’m sure this is an elementary question to most, but we have not had this much size difference in a brood over the years; my wife adores these little houdans and I want them to be as healthy and safe as possible. pic posted is size difference of the smallest of the 2.