After reading all these stories, I though I give you a wake up call.
The two families are as different as Black and White.
Karabelas (correctly spelled Karabellas) is a over 1,000 years old Venetian name CARAVELLO. The family, one of the aristocratic families of Venice, originates from Jesolo, a little place just outside Venice. Around 1210 members of the family resettled in Crete and played a very prominent role there Leonardo Caravello was Duke of Crete 1429-1432 and there are others. Theodoros Karabellas was a "Notar" in Heraklion 1642-1644. In 1669 when Crete fell in the hands of the Turks, George Karavellas, son of Emmanuel, escaped to Zante. He was calling himself as Genarchis of the family "Karvellas". etc. etc and the rest is History.
The name Karavellas should not be confused with the name Karampelas which is of Turkish origin (Karas = Black).
Regarding Kourbelis, I can tell much because my computer broke down last year and I am to slow in revering data. However, I can say, There is NO village called Kourba or Kourbe or anything like ti in or near Mani. In fact the name is most likely incorrectly written (There is a name Korovelis --> Korvelis from Smyrna. I will probably know the answer when I recover all the data.