To Kill a Mockingbird/WMG

Boo Radley is a Heroic Albino.
When Scout finally meets him in person, he is described as being ghost-like, with very pale hair and skin. Scout, not knowing what albino is, would just assume this is because he stays inside all the time, rather than Radley being born like that. This would also explain why Radley is familiar with the doctor; he probably would have medical problems which often come with albinism like bad eyesight. It might also be partly why he lives such a reclusive life, as if he was an albino he would be easily identifible in a small town and rumours could spread easily about him, (especially in 1930's Alabama).

Bob's kids have different mothers.
Although Bob Ewell sexually abused Mayella, the story has never mentioned her being pregnant. So maybe she isn't the mother of the kids. Bob maybe had kids with various prostitutes.
 * Except he doesn't seem like the sort of guy to take in bastard children who could potentially have had other fathers. Also, Maycomb doesn't seem like the sort of town that's swarming with prostitutes.