Cut away the eyes and mouth of a jack o’lantern from the front of the oranges. Cut the top from each of the oranges and carefully scoop out the inside and placing it in a bowl. Squeeze the orange flesh to retrieve 2 ounces of juice.
Whip the heavy cream and sugar to stiff peaks. Add orange juice to the sour cream and stir to fully combine. Add the orange sour cream to the whipped cream and fold gently to combine. Add 1/4 cup of cream to the bottom of the oranges. Fill the remaining space in the oranges with blueberries and blackberries. Refrigerate until ready to serve.