So I'm running a Pathfinder campaign and my party is going to have to deal with Royalty a fair deal, and I'm just wondering something about forms of address/titles.

First: Do the siblings of the reigning monarch have any default titles, assuming they aren't assigned lordship over somewhere? Like, what would you call King Tim's brother? Just Lord/Sir or would he have a particular title?

Second: What is the title of the child of a reigning noble who is not the king/queen? Like the Duke and Duchess of Placename have a son. Is he just addressed as Lord/Sir, or does he have a specific title by virtue of being the duke's son?

Obviously forms of address and titles of nobility vary from place to place and time to time, so feel free to just rattle off relevant titles from different points in Western European history or whatever you think would be best suited for a generic fantasy timeperiod setting.