I know this sounds really far fetched, but remeber how Hui Kyung mentioned going to visit his oldest brother's grave? And how his mum started talking about this incident when Jae Kyung was younger and was worried and was stopped by her husband? Being the psychopath he is, is it possible that Jae Kyung may somehow be responsiblle for the oldest brother's death?! I mean, that way he got to inherit the company and everything...