I will cite the example of Solaria again because the situation with the Ducny of Sun Hall joining Luria Nova is IDENTICAL. That was ruled legal. Its a power play, not a realm merger. You're allowed to do dastardly things, which this was. This is not two sovereign entities becoming one. This is a Duchess making a power play. There is already a set precedent. Go read the Solaria/LN realm merger case.
Can you give me a link? I am not being lazy, I genuinely can't find, albeit I might be able to when I am not so tired.