Create a new rule entitled “Titles”:

A Noble may hold one or more Titles. Titles are divided into three Ranks which are, in descending order: Dukedoms, Earldoms and Baronies. A Noble who holds a Dukedom is Duke of that Dukedom; the same holds for Earldoms and Earls, and for Baronies and Barons. It is proper, but not required, always to address a Noble by their name, followed by their title or titles with the highest Rank, optionally also listing their other titles in descending order of Rank.

A Dukedom may hold Lordship over one or more Earldoms. An Earldom may hold Lordship over one or more Baronies. If a Dukedom holds Lordship over an Earldom which holds Lordship over a Barony, the Dukedom holds High Lordship over that Barony.

If a Title holds Lordship or High Lordship over another Title, the Nobles who hold those Titles may be referred to as each other’s Lord and Vassal, respectively. This is only true if the Titles are held by two different Nobles. A Noble may be Lord and/or Vassal to another Noble through more than one Title.

The Peerage wiki page denotes the available Titles and their hierarchy. Titles which are not currently held by a Noble are Abeyant.

Create the Peerage wiki page (if it does not yet exist) and blank it.