Ryan Raburn and Brandon Inge hit grand slams as the Tigers defeat Oakland, 14 – 1. It is the first time that Detroit has hit two grand slams in one game since Jim Northrup did it all by himself on June 24, 1968.

On May 15, 2009 — Ryan Raburn and Brandon Inge hit grand slams as the Tigers defeat Oakland, 14 – 1. It is the first time that Detroit has hit two grand slams in one game since Jim Northrup did it all by himself on June 24, 1968.

Source:
Baseball Reference May 15