Prepare a grill or grill pan for medium heat; oil grates. Grill peach, plum, and nectarine halves, flipping once, until lightly charred and tender, 8–10 minutes. Transfer to a cutting board and let cool, then cut into 1" chunks.
Muddle grilled fruit and 6 halved cherries in a large pitcher with a wooden spoon. Top with wine, orange juice, brandy, and simple syrup; stir to incorporate. Chill at least 1 hour.
Fill glasses with ice. Add sangria and muddled fruit and top each with a cherry.
