I'm the guy who messaged you on Steam for some suggestions I had for a particular character start. Byzantium, 1124, Ioannes II.
First off, the man himself. He has one scripted trait, zealous, and his other two traits and education are randomized. I would suggest the randomized traits be replaced with forgiving and brave. Zealous is fine, as he was known for his deep religious convictions and persecuting Paulician and Bogomil heretics. Forgiving is absolutely essential to his character too; he has been dubbed the "Byzantine Marcus Aurelius" because he was reputed to have never had anyone tortured or mutilated. He also forgave his sister, Anna Komnene, and her husband Alexios Bryennios for plotting to overthrow him (albeit with Anna being unofficially banished to a monastery). He should be brave too, as he frequently led his armies in combat, receiving a wound in the Battle of Beroia and personally operating siege equipment at the Siege of Shaizar, in which he is praised by both Latin and Muslim sources for his personal courage.
In a similar fashion to brave, above, his education should be fixed at tier 3 military (he was good, not phenomenal) and - for added flavor - he should be given the siege engineer commander trait. Historians both contemporary and modern agree Ioannes II favored sieges over pitched battles, recognizing the random nature of the latter and the relative safety of the former.
For even more flavor, the character Ioannes III Axuchos (correct spelling should be Axouchos), Duke of Moesia should be scripted as Ioannes II's best friend. The contemporary historian Ioannes Kinnamos writes that he was Ioannes II's only close friend and personal confidant, and from the sources you can really see how close they were. Axouch was a Turk had been taken as a slave by the crusaders at the Siege of Nicaea and given to Alexios I as a gift, who placed him in the imperial household, believing he would make a suitable companion to Ioannes II. When Ioannes II came to the throne, years later, he immediately made Axouch megas domestikos, which was commander-in-chief of the Byzantine military and second only to the Basileus in rank. When Ioannes II foiled the plot of his sister Anna to overthrow him (see above) he tried to give estates he'd confiscated from her to Axouch (who wisely refused). Ioannes II also commanded that petitioners - even members of the imperial family - make obeisance to Axouch as if they would to himself. Dudes were really tight. Naturally, as megas domestikos and commander of the Byzantine military when Ioannes II wasn't around, he should have a fixed military education as well.
Titles. Right off the bat, none of Ioannes II's family should be title holders (same for Axouch). In the Komnenian period the semi-feudalization of the empire that was characteristic of the Palaiologian era had only just begun and Ioannes II is noted as shying away from making the empire a "family business" like his father, Alexios I, allegedly due to his experience with his sister's attempted coup. The imperial family did not hold lands in the same way Western royal families did. While they were given military commands and there are references to them holding private estates, as with CKII the way the game is set up it just doesn't work. Further, while we have some listings for historical holders of actual IRL titles (that may or may not exist in-game), none of Ioannes II's children or siblings are recorded as holding any of the titles they do in the 1124 bookmark. It makes the setup look glaringly ahistorical because his children and siblings are scattered across the map like Western feudal vassals (which they absolutely weren't), and the underage future Manuel I would certainly not be given a province to hold as military commander.
Unfortunately I cannot tell you who should hold the titles currently owned by the imperial family at game start. Ioannes II's reign is, unfortunately, poorly recorded compared to his father and son and we do not know who holds governship of those particular cities or Themes. I would suggest randomly generated Greek Orthodox men as the closest we'll get.