Shade of the Tree — Piers Anthony

The estate was Joshua Pinson's inheritance from his oddball uncle Elijah: isolated in the deep Florida woods, with a half-built solar house stocked with enough supplies to weather a siege. Josh decided it was time to rake his two young children away from New York and the memories of their murdered mother. Time to make a new life in sunny Florida. There was just one thing that Josh hadn't counted on.

The place was haunted.