Benny Ramírez and the nearly departed / José Pablo Iriarte.

Enhanced descriptions from Syndetics:

Benny Ramírez can see dead people . . . Well, one dead person, anyway. A hilarious and heartwarming story about a boy who can suddenly see the ghost of his famous musician grandfather!

After moving cross-country into his late grandfather's Miami mansion, Benny discovers that the ghost of his famous trumpet-playing abuelo, the great Ignacio Ramírez, is still there . . . and isn't too thrilled about it. He's been barred from the afterlife, and no one can see him except his grandson. But Benny's got problems of his own. He's enrolled in a performing arts school with his siblings, despite having no obvious talent.
Luckily, Abuelo believes they can help each other. Abuelo has until New Year's Eve to do some good in the world and thinks that teaching Benny how to play the trumpet and become a school celebrity might be the key to earning his wings. Having no better ideas, Benny finds himself taking Abuelo's advice--to disastrous and hilarious results.
Benny and Abuelo will find that there's more than one way to be great in this unforgettable, laugh-out-loud tale of family, music, and self-discovery.