Kastro-Larissa (or Argos...which is the modern name) is owned as a fief "Lordship of Argos and Nauplia" by the noble family of Brienne who also held the "Duchy of Athens", but lost it to the Catalan Company....
Walter IV was also briefly the ruler of Florence... that was the idea to put Kastro-Larissa under florentinian control.... but he was deposed in 1344 (just before the beginning of our mod) so the region will be left rebel....
Constantinople, as well as some coastal cities and islands, are held by the "Imperial Regency" faction... all other possetions of the empire are controlled by the "House of Kantakouzenoi" faction.... In reality both Kantakouzenos and the other Regents (Apokaukos, Patriarch) are competing for the guardianship of the under-age John V Palaiologos... they are all explained in the Introductory text above the pics in the 1st post...