How do I quit being a russian Tsarina and turn swedish?
Unfortunately, I don't think that such a way even exists. In the world of Mount&Blade (any game of the series) there is no way to stop being a faction leader with the only exception of being overthrown/your entire faction dismissed and leave the land.
Yes, diplomacy of M&B is strange. Sometimes it's very strange. But all you can do is to install some mod and hope for the best or deal with existing problems.