Im a newbee... no real knowledge, so please correct me if im wrong, im learning too.
I see it it as they dont have enough space. The bottom box should be brood in a circular shape within the frames then with honey on the sides... you say theres an empty frame... but you dodnt say where the empty frame is... depending where its at in the box it may need to be switch with another frame in that box to promote growth.
Then another box on top seems like a good idea pretty soon to encourage growth as the queen like to build brood and lay upwards. This would encourage building the colony bigger.
After the second box is built up and strong id assume then to add a queen excluder and honey super for excess honey building.
However i have seen people only use one hive body, then ass queen excluders and supers on the top for honey the first year... however i tend to disagree with that and help the colony grow bigger and strong firat before worryimg about excess honey to harvest...
Just my two cents, but by all means i could be way off..