Ghostmobile, The (Vintage Paperback) by Kathy Kennedy Tapp

Ryan's new friends are ghosts! 

When Ryan and his family arrive in Wisconsin, he's convinced his life is doomed. No best friends. No ball games. No biking on the beach. Just a lot of getting back to nature. What a summer! 

But that's before the Ghostmobile rolls into Ryan's summer. He's never seen anything like it - and he's never met anyone like Aunt Vira, the ghostly librarian, or her nutty niece, C.C. 

Aunt Vira and C.C. want to get out of their ghostly rut. Ryan and his brothers and sisters are just the ones to help. All they have to do is keep the Ghostmobile a secret, follow Aunt Vira's crazy instructions, and solve a 50-year-old mystery. 

This will be one wild summer after all!