This. Vanille and Fang could not have been born when Cocoon was created so therefore their "husbands" could not have gone to live on/in it.
Also, when does it say that Fang was married? I'm only on Chapter 11 but I'm pretty sure it would have been mentioned by then. And if Vanille weren't married it's probably safe to say she didn't have a kid, so she couldn't be Nora's mother, not to mention that would to mean Nora was like 300 years old.