"If anything her family is self-made" I think this is a mistranslation. My guess is the original text must be 자작 (Jajag), that means "Viscount". Well, Jajag also means "one's own work, cultivation of one's own farm, self-service", but in this kind of historical setting, it clearly means "Viscount". It's not that important but would make more sense for the plot since Elena comes from a Viscount's family with nothing but the noble title. There's no way a Duke's son, even for a third son, to get a benefit from union himself with her.