Lay out one pie crust on a baking sheet lined with parchment or on a baking stone, leaving room for the second pie crust next to it.
Mix together the sliced peaches with half the blueberries, 2 tablespoons of the flour and 2 tablespoons of the sugar in a bowl. Pour over one pie crust leaving a 1-inch border. Fold up the uncovered border over the edge of the fruit and pinch into pleats. Sprinkle the crust and fruit filling with 3 tablespoons of turbinado (or raw) sugar.
Lay out the second pie crust on the baking sheet. Mix together the sliced strawberries, the rest of the blueberries, 2 tablespoons of flour and 2 tablespoons of sugar in the bowl. Pour over the second pie crust and form the galette the same as the first. Sprinkle with 3 tablespoons of turbinado sugar.
Bake in preheated oven until crust is lightly browned, 12 to 14 minutes. Sprinkle with more sugar if desired. Serve warm or at room temperature.