Skyblade,the citizens of Cocoon came from Pulse actually.
Scorted by the Fal´Cie.
So at which point would they deny access from the outside?
After finishing the shell?
Would they(The Fal´Cie) not welcome new persons?

It's just something you made up from 2 things that happen to match. Dysley wears blue, so he must be from the Yun clan. Fang and Vanille are old, chronologically speaking, so they must be somehow - by huge coincidence - direct ancestors of the other main characters.
I completely agree with you on this one.

But the Nora subject was proved beyound doubt.The only thing that stand in the middle is your insistence concerning that being a possible coincidence that Square intends.
When it is obvious that Square was hinting something here concerning Snow and Nora´s relationship.