My Sister's a Nightmare (My Sister #6) by Gretel Killeen

When tiny Eppie and tiny Zeke finally manage to escape from a book they accidentally end up in a rattling carriage that is part of their mother's train of thought. Unable to get off at Read World. Dream World or even Fantasy World. Zeke and Eppie find themselves hurtling toward their mother's ridiculous nightmare. What follows is a laugh-till-you-split-your-sides adventure. Full of googly ghosts, drastic draculas, spiralling spiders, haunted houses, vampish vampires, disgusting meals that never ever end. Will Zeke and Eppie escape from the nightmare or will they be stuck in their mother's bad thoughts forever (along with the boyfriend she had when she was nine and a packet of chocolate biscuits)?