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 preheated oven 45 minutes to 1 hour.