Peel and slice sweet potatoes. Put in a large pot of lightly salted water. Bring to a boil. Boil 5 minutes, drain and cool. Put sweet potatoes into a 2 quart casserole, dot with the butter. Mix sugar with next 8 ingredients and mix well. Sprinkle over sweet potatoes. Pour orange juice and lemon juice over sweet potatoes. Cover with the sliced oranges. Bake in a preheated 350-degree oven for 45 minutes to 1 hour.