Fablehaven
A fantasy series that has five books and is about two siblings who get assigned to either the light or dark side of magic. They still have to be a team even though they're on opposite sides. The sequel series is called Dragonwatch.
'I got the dark side. My sister got the light side. We're like a broken pair of socks.'
'This book is stupid, but I still read it.'
'I can't believe we still have to be a team even though we're on opposite sides.'