If we go for a variant of option A (either option A or the reverse of it) the rules about giving out land need to be made stricter. I understand that a lot of human political RP is about securing rallies by giving land to people who themselves hold a rally, but most of the human nations are dotted with tokenist cities, towns, settlements, castles and keeps.
Condense the pro Orenian Tahnic nations into one city, perhaps a town or one or two villages, one or two castles, one or two smaller keeps.
As the anti Orenian forces are spread amongst other races that wouldn't feasibly move into one nation, they could be moved into a town, a castle and one or two keeps.
The excess land can then be lopped off by seismic activity that also damages inactive RP hubs in the land that isn't being removed for some fun adventuring.
Conditions should be discussed with both sides first ofc, but a fractured Tahn could give a pretty cool thought to why Asul and Ceru are separate; Axios is an unstable land mass. Another bonus is that it gives us reason to want to leave; it's dangerous with the tremors. Another bonus is that 6.0 could be styled around one of the older land maps, possibly fractured like Axios, possibly sunk into the ocean, possibly raised, though the ruins would give so much more flavour to the land; there was nothing quite like exploring the Dreadlandic ruins near Courland.
TLDR: Condense Oren into smaller space, condense rebels into smaller space, earthquakes split Tahn and/or Asul+Ceru, destroy unused land and damage unused settlements.