I'm guessing that the OP does not controll all holdings in the duchy's.
Check each county, if all Baronies are a part of your realm. You or your vassals need to control ALL holdings in the mentioned duchies, to recreate The Roman Empire. (most of the time the Hashasadins have a barony in The Duchy of Antioch)
Check each county, if all Baronies are a part of your realm. You or your vassals need to control ALL holdings in the mentioned duchies, to recreate The Roman Empire. (most of the time the Hashasadins have a barony in The Duchy of Antioch)