Thanks for the update. I'm not experienced in cold weather (Vic) overwintering, but there are a couple of reasons I can think of you might need a new queen. If the queen is a new supercedure you might have to wait a week or so in case she hasn't started laying. If this is the one which has been there a while without laying she could be a problem as they are obviously still foraging very well and haven't shut down yet. So bees will be dying earlier and not replaced, and numbers will go down. And your other hives still have brood so that is an indication. But can you still get mated queens this time of year? You could put brood frames in because it sounds like there's no place for a queen to lay now.
Think my supplier still has them, will keep an eye out and see how they go, i think brood from another hive would get chilled with the 10 min drive to the other site.