The Whizz Pop Chocolate Shop by Kate Saunders

Oz and Lily Spoffard, along with their parents, inherited a house with a family business (a chocolate shop).  Apparently the house and shop are reeking with magic and to their surprise, so are Oz and Lily!  As they discover their family's magical history, they experience a summer vacation beyond their imagination.
A talking cat and smelly yet endearing rat show them the ropes of SMU (The Secret Ministry of the Unexplained).  The SMU need the twins to stop a terrorist group from finding a chocolate recipe which will make them immortal.
Exciting!
Grade Level Equivalent: 4.8
Points to discuss/warnings: pg. 84 The Uncle Isadore swears.  The children and their uncle are technically witches.  Magic is abundant.   Ghosts and goblins frequently make appearances.