Pure Dead Magic by Debi Gliori
All is not well at StregaSchloss, home of the bizarre but lovable Strega-Borgia clan. Mum's attempts to improve her witchcraft skills are failing miserably. Dad has stormed out in a fit of pique. Titus is virtually umbilically attached to his computer. Pandora is seriously bored. And Baby Damp is getting her fat little fingers into everything around. Enter wonder-nanny Mrs McLachlan - she'll soon sort out the Strega-Borgia children, and their parents too, but will she cope with the presence of mythical beasts in the basement, to say nothing of the unexpected arrival of four hit-men, including one in a rabbit suit?