Preheat oven to 400F. Line a baking sheet with parchment paper. On a lightly floured work surface, press crusts together and roll out to a diameter of 14 inches. Transfer to parchment-lined baking sheet.
Cut each peach into eight slices (24 slices total). In a bowl gently fold cut peaches and berries together with 1/4-cup sugar to coat, being careful not to crush berries. Gently spoon fruit mixture in to the center of the pie dough round and spread out from the center to about 10-inches. Fold the edges of the piecrust dough up over the fruit, pleating the edges as you go around.
Whisk together egg yolk and water. Brush pleated edges of pie with egg mixture and sprinkle the remaining tablespoon of sugar over crust. Break butter into small pieces and place all around the pie. Bake for 30-35 minutes or until the edges are golden brown.