I think the whole thing with the grandma favouring Wiwaa is mainly cause she's used to getting her way, with her dad not getting the fortune it could also be that he declined it and her parents don't like going against the grandma because they wouldn't get anywhere with her she's stubborn and it would be like repeatedly walking in to a wall. I think that she's kind of moulded Wiwaa in to her miniature, like they're both very stubborn and have unpredictable tempers, and maybe she wanted to raise Wiwaa because she never got the chance to have kids since the one guy she fell in love with ended up falling in love with someone else and thus totally turning her off all guys cause they're apparently all lying gold-diggers. So since she was able to have like a kind of daughter she let Wiwaa's parents raise Jao Kah, but cause she's young and also too happy and bright and like not as stubborn as Wiwaa she doesn't pay much attention to her. I just get the feeling the grandma is very used to getting her way and must have been a very spoilt child for her to turn out the way she currently is, I wouldn't mind if she got kidnapped somewhere for a few days just so Ah Poon didn't have to get put down just cause he doesn't carry the same blood as her.