Having two coops is a plus. Having an area to free range is good. If you leave the chicks and Ruby in the second coop and they can talk through the wire for a week or so. When you can let the older ones free range together while you are there to watch. There may be some strife as they decide...
What Is your current arrangements? Are the week olds by themselves or with the rest? It would might easier to introduce her first to the week olds. But neither introductions can happen overnight without some strife. If you can pen them next to who ever you decide to put her with for a week or...