Three Spirits of Vandermeer Manor, The (Mostly Ghosts #4) by Mary Anderson

"...a double-barreled mystery filled with chuckles and shivers. Great fun!" 
-Joan Lowery Nixon

Amy and Jamie are twins. Jamie is brilliant and logical, while Amy is psychic - an ability she keeps hidden from everyone but Jamie. One day she realizes she can communicate with a spirit from the Revolutionary War...and his advice is sometimes misleading, often helpful, and always exciting. 

When their Uncle Harold restores the Vandermeer Manor, the twins experience some mysterious beings during their visit. Is it possible the old house is haunted?