Heat one side of grill to medium-high 350°F to 400°F. Place peaches in a large bowl. Stir together sugar and next 4 ingredients in a small bowl. Sprinkle mixture over peaches, and stir gently to combine. Spoon peach mixture into a buttered 10-inch cast-iron skillet. Cut 2 tablespoons butter into small pieces over peaches. Cover skillet tightly with aluminum foil.
Place skillet over lit side of grill, and grill, covered, until bubbling and hot, about 15 minutes.
Biscuit Topping: Stir together flour and next 2 ingredients in a small bowl. Make a well in the center, and add cream and melted butter. Stir just until mixture comes together. Uncover grill, and discard foil; dollop peaches with dough mixture. Cover with grill lid, and grill until biscuits are browned, about 15 more minutes. Remove skillet from grill, and let stand 10 minutes before serving.