You say they are not very strong. If you only have 5 frames of bees in the brood box and the other frames just have a few on them, you need to remove the medium, freeze and save the honey frames for feeding back to them as needed. I am assuming the top medium is just an empty box to cover a feeder. And yes, I have used med. frames in a deep for feeding in the winter. Consolidation of bees is the best defense I have found for most intruders. From your description, it sounds like you found a moth in the top box, the bees may have kept it run up there. It only takes a about a week for the worms to ruin a weak hive. Keep a close eye on it. I have moths and SHB here year round. Just remember moths won't/can't take over even a 2 frame nuc if there are enough bees to patrol it. As long as the queen is laying well, I prefer consolidation to combining.