I don't know the answer, but Carolos Baerga was the first MLB to hit two homeruns from different sides of the plate in the same inning of a game (1993).

The record that will never be broken is Tatis (I think) hitting two grandslams off of the same pitcher, Chan Ho Park, in the same inning. Why will it not be broken? No manager will ever be dumb enough to give up a granny, load the bases again, and then allow the same pitcher to face a guy who had homered that inning.