Davis even becomes the fellow who introduced Grandpa to Obama Sr., and he to his sister.
That way you end up with the correct genes in the right person.
BTW, this is not original with me. When the Birther movement first showed up that's one of the theories.
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.