Just because a character's family history comes up doesn't mean five pages of backstory are justified. If you involve a character's sister, what happens during the game with her is much more important than whether she once urged the PC not to marry someone who ended up becoming an evil warlord and was then killed by the PC.
Sure, the evil warlord ex-girlfriend could come back as a death knight or something, but you're not going to do this for each and every background detail included.
There is a line between hooks and trivia. While you can elaborate as much as possible, if the charater's life so far, in summary, can't be comfortably encapsulated in a paragraph, then something has gone wrong.