It makes me wonder if Familial bonds are the only thing holding the twins together or is part of their bond just from necessity. Once its possible for one of them to take the throne of the 6 realms without the other, I think they will do it. For now the twins need each other for quite a wile longer and are ok with each others existence, no real fighting between them. But as they build the joint nation up, their factions and arrogance will grow and get to a point where they don' t need the other. When that point happens, Rowan will choose one of the two or go independent.That's what I'm aiming for as well. A power couple almost like the twins. Rowan handles the military aspects while Alexia handles the magic and subversion.
I think Shaya would side with Jezera, Skordred with Andras, and Alexia, Clionha, Greyhide, Liurial, and Helayna would be more inclined to side with Rowan (depending on ifluence). On Rowan's side, Clionha would probably be the most key figure as he probably needs her help to split off from the twins.