Stanley Ann didn’t seem to have a strong maternal instinct, and seemed to care more about her studies than her family, so why saddle herself with a baby half-brother just as she goes off to college? Not to mention a husband - makes dating a little difficult, even if he’s far away and estranged. The baby is a more practical difficulty, anyway.
Again, where was Sister Obama? travelling with her brother? no, money was tight for him. And if Sister Obama looks like her brother, you’re still not going to get O Jr’s features.
The skulls do not match.