The Divorce
Lyle Raymond

It became fairly clear to me early in the first season that there was a subtle and mildly disturbing reality underneath all the good-natured scenes at Brendon's home. Let's look at the facts:
a.. Josie is mulatto, but Brendon has red hair.
b.. There is a significant age difference between Brendon and his sister.
c.. Paula doesn't seem to hear much from Andrew in Season One, and doesn't seem to hold it against him, either.
d.. Paula likes to drink...maybe a bit too much.
Assemble these and perhaps a couple other tidbits and you have a recipe for an intruiging backstory:
Andrew found himself increasingly distracted from his promising career because Paula's budding alcohol problem was causing her to neglect domestic responsibilities. The issue finally came to a head when Paula (confessed to having)/(was caught in) an affair with a young man of African descent (likely, since the neighborhood is somewhat culturally integrated). Andrew divorced Paula, leaving her with Brendon and his newborn, illegitimate sister. The whole experience sobered her up, mostly, and she has since learned more or less to keep the household running smoothly.

NOTE: This was originally written around "Temporary Blindness", the show creators figured out the mystery for us by revealing Josie was adopted. (thanks to Judy for mentioning this mistake)