skygiants

I think that was the story in Mary Stewart's head, until someone pointed out that children of identical twins are genetically even closer than normal first cousins, so she made the hero a nice safe second cousin adopted into the twin uncle's family. This gave the bonus of making him heir to the senior position in the Family Merchant Bank, and even richer than his adoptive father and uncle.

I think the book stuck in my mind so well because of the tourist's eye view of a lovely land, when I was reading grim newspaper stories of civil war.