My family and other ghosts - Lou Kuenzler

10 year old twins Ivy and Ash didn't expect to be visited by the
ghost of their Grandpa Digby (who they've never met) on a stormy
night. They definitely didn't expect him to announce that they have
a home in Darkmoor (VERY different to Dartmoor), and that he wants
them to come and run it as a hotel.
They persuade their dad, an 'experimental' chef, to move to Grave
Grange, a crumbling-down higgledy-piggeldy hotel, but decide not
to mention that it's VERY haunted.
As they try and save the hotel, chaos ensues, and soon they must
save their new spooky friends or risk losing their home for good...