Mom is right out. While the sister's situation was left open at the start of the game (in fact, using the hoary old method of being assumed dead but with no actual definite body, which by story logic would virtually guarantee she's alive), Moonbox has apparently said on several occasions that she will also not show up. So, if two aunts, a cousin, a couple of people who served as foster moms of a sort (Jamila of course, but Jada also seems to have filled the role somewhat), and Nana aren't enough, I guess you'll have to just hope you have someone out there who's attracted to the MC who, unbeknownst to either of them, is his half sister or something.