Read this link, it really clears things up on who is who and who outranks whom.

Another link that has foreign titles included.

Bulgaria on the SS map consists of Sofia and Targoviste, although we've held Tessaloniki in the past as well. In order for one to be dubbed Duke of Bulgaria he must be the Baron or Earl of both Sofia and Targoviste and must be approved by the King.

On the subject of how it is proper to address someone, read this page.

In short, the King is addressed as "Your Majesty" or in some instances as "His Royal Majesty", the King's children may be addressed as "my Royal Highness". Dukes are addressed as "Your Grace" in England and as "Your Highness" in most other countries. Everything below - Count, Viscount, Earl and Baron are Lordships, ie. "my Lordship" or simply "my Lord".

You can't all be Dukes. This title is reserved for close relatives of the King or those of his closest friends he has elected to Dukedom. In fact the only one who is fitting to be a Duke is Bokeny and only if he is granted a nice city to be Duke over it's province. Like Constantinople or Tessaloniki.