Same realm can even sometimes offer different experiences. Same continent, and it's an entirely new ball game. Working two different characters towards two different goals using extremely different methods on BT in the 4th Inv was one of the most exciting things I've experienced in my 3.75 years of playing. Aside from that, we are what we make of our stories. Some things are governed by the rest of the realm or continent, while a lot also has to do with our own authorship. But everyone's different, so while some players might enjoy playing two radically dissimilar characters that might even fight each other, some other players might enjoy playing two close family members who mutually support each other through all difficulties. The list is almost endless of different styles.
As far as having both characters on a single continent, and even a single realm become the dukes of its only two cities, if the realm actually does that, then so be it. There's nothing saying that one can't have two characters in a single realm both as dukes. If the realm has some fairness policy, that's Coria's decision. But as far as I know, doubling up as duke is not against any spirit of the game.
