As for your expecting chicks, I'd separate them when they hatch. Some breeds do fine with new hatches in the run and others don't. Since you have such a variety, I wouldn't take the chance.
Your BO chicks should be big enough to place together with your old flock, even if they aren't fans of each other. They should be fine. You may have two flocks in the same pen. I do now.
Sorry Nireklov! My mom lost most of hers to a dog recently. Only one was left. Now she is going to reinforce her coop with extremely thick wire and lock her girls up every night.