I opened all the hives today to look inside. Apart from the issues caused by queen exclusion, everything seems to be going well.
Hive G is building comb and looks healthy.
Hive F is building comb but still dropping lots of Varroa.
Hives C, D and E have space and show evidence of recent comb building.
They're all going well. I still see no evidence that any of these colonies swarmed to produce Hive G. I assume that it was a coincidence. That means that it has not come from an untreated colony.