If you want you could tie it down to rank in faction (and possibly add ability for faction leader to choose the name set to use)
Like European set could be:
King, Duke, Margrave , Count, Baron, Baronet or something like that
or a nordic set could have Jarl replace multiple of those and could add Thane or something for the lowest rank. You probably want to make it so that there are maximum of 3 or 4 different titles so there's more consistency.
You should probably allow the clan leader to choose his title freely from a list of fairly plausible titles (Emperor, King, Sultan, Khan, whatever)
So the basic idea is that clan leader will be King or something, the officers would probably be Dukes or something like that and if a lower rank player happened to get a fief they'd be Barons or Counts or something lower.
