Ok, so I'm a little confused here. Is Mab another sister or she separate fairy?
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Is there another reference that connects Mab to the fates or WOD?
I don't think there's anything in game that connects Mab to the extended ruling family.
I think the real history was that Edgar isn't really Obertitan's son... they kidnapped him from someone else, :p... This might explain why all of his "relatives" could care less if he gets kidnapped by someone else, as he was never related to them. It might also explain why he's said to be "human" in KQ4 related material.
By real history, do you mean real world references to Oberon and Titania (and their interest in changelings, etc.)?

I think in game, it's heavily implied that in the KQ universe, Edgar is their biological son. As for his lack of green skin, he just takes after his dad's side of the family (whoever they are). References to him as a human can be easily explained in two ways: 1) look at Genesta and her entourage--a pretty striking feature there would be the wings--and 2) since he looks human, why assume he's a wingless fairy person from another dimension when he could just as easily be human. On top of which, I think the only thing clear from the end of KQ4 is that there wasn't exactly a plan for Edgar at the time... which reminds me... what about that KQ4 remake, eh? *wanders off on the internet for a little bit*
The secret is who controls Edgar will rule the world. He is the living embodiment of Macguffin. Rosella will now be able to rule the universe (well she could if she wasn't in a coma). Shadrack was trying to prevent that from happening.
hrmm... but why wouldn't Shadrack have taken Edgar with him then, after all everyone else has kidnapped him?
One Edgar to rule them all, One Edgar to find them,
One Edgar to bring them all, and in the darkness bind them
... in green skin... ~The Edgar Strikes Back