So, the Sicilian Kingdom is born becouse, Ruggero di Altavilla the sicilian Count and his cousin Guglielmo di Altavilla had  a bad relation, and then in  1127 when he died Ruggero had Apulia (ducato di Puglia) in junior partner. And in 1130 the first Kingdom of Sicily was formed. Now, this is a game,  i did about 20 games with Byz at speed 5 ignoring all the situations and Sicily never formed in 1150, Apulia just took all the lands and stop. But this is a lot contraddctory becouse storically the Sicilian kingdom was one of the most important kingdom in italy. So in my opinion you could add this kind of event: Family Issues (Apulia has no heir, country is trinacria, is 1100) duke of apulia dies, apulia becomes  trinacria junior partner.
Also i think there should be possibility to form Trinacria, becouse Trinacria was the first name of sicily, but you can't form it in this mod (just by rebels) So a mission could be: Unify Trinacria. (country has Sicilian as main culture, own core Palermo, Agrigento, Messina, Catania, Siracusa)
(also Sicily does not exist)
Most important events in the kingdom of sicily are basically 3. The Kingdom had a lot of domination, but this does not matter in the game, becouse you know, is a game, and there should be difference. But one is very importat. I am talking about "La rivolta dei vespri Siciliani" the target of this rebellion was the Angiò-De Valois house. Storical effect are basically 2. Kingdom of Sicily went free from the De Valois occupation. And also Angioini house (in 1227) stopped the balkans conquest against byz. So an intresting event could be: Animus Tuus Dominus (country is Sicilia) +15% local autonomy in all cored province + 13 pretender rebel in Palermo.
The second event is a cultural event. That could fire in 1170-1260. I am talking about the sicilian school. Storically this was the first "school". It was a literary movement that influenced all the poets in Italy. Sonnet was born in sicily. And "sicilian was the main language of all Italian region" - (Dante Alighieri, De Vulgari Eloquentia), and also gave to the emperor Fredrick I a lot of merits. . Unfortunatly when the Hohenstaufen house fall down with Mafred the Sicilian School stop his existance. Event: Sicilian School (fires in 1170) Catania gain base tax 1 -  base manpower 1 - base production 1. Till 1260 +1 yearly prestige (if hre emperor also +5% imperial autority)
Also an intresting event could be a forced Royal Marriage with Aragon (if both exist of course) that is the third important sicilian event. When Sicily gets under Aragon. But of course is nosense adding this is the game
(sorry for my bad english. I am not so good.)