The Orphans (spoilers)

[Goldenboko]

But in FFXIII most of them are orphans.

Depends on your definition of Orphan or more specifically whether or not there is an age limit, in FFXII Vaan and Penelo where both Orphans, Balthiar became an Orphan after he (SPOILER)killed his father, Ashe became an Orphan when her father was murdered, Basch could be considered an Orphan as he abandoned his family to serve Dalmasca, and Fran could be considered an Orphan abandoned by The Wood. Boom, every freaking main character.

Not every person on Cocoon is an orphan.
Coincidences don´t exist.

I agree, but Cliches do exist. Main heroes and heroines being orphans or orphaned is an overused plot device to free the heroes from responsibilities and is the reason Square uses it all the time.