The Angels defeat the A’s, 9 – 8, despite home runs by brothers Jason and Jeremy Giambi for Oakland. Vladimir and Wilton Guerrero of the Montreal Expos were the last pair of brothers to homer in the same game.

On May 8, 2000 — The Angels defeat the A’s, 9 – 8, despite home runs by brothers Jason and Jeremy Giambi for Oakland. Vladimir and Wilton Guerrero of the Montreal Expos were the last pair of brothers to homer in the same game.

Source:
Baseball Reference May 8