Family?

What if when Regina cursed Rumple, she gave him a 17 yr old sister named Sybelle. How would that change his relationship with Belle? How would this change the story? Who was she and why was she made into his sister? What's she hiding? How does she fit into his story and that of Zoso the Dark One before him? Why was Rumple chosen to be the next Dark One? Nothing was left to chance.