Johnny and the Dead (The Bromeliad Trilogy)

The second hilarious fantasy novel about Johnny Maxwell from master storyteller Terry Pratchett.
Sell the cemetery?
Over their dead bodies.
Not many people can see the dead (not many would want to). Twelve-year-old Johnny Maxwell can. And he's got bad news for them: the council want to sell the cemetery as a building site. But the dead have learnt a thing or two from Johnny. They're not going to take it lying down... especially since it's Halloween tomorrow.
Besides, they're beginning to find that life is a lot more fun than it was when they were... well... alive. Particularly if they break a few rules.