1. Place 10 pop sticks in a bowl of warm water.
2. Using a sharp knife, slice off the top and bottom of the oranges. Working from top to bottom, slice off the peel, removing as much of the white pith as possible. Slice each orange horizontally into 5 round slices. Remove any seeds or pith in center of slices.
3. Drop half of pineapple pieces into bottoms of ice pop molds. Place a slice of orange in each mold and top with remaining pineapple. Pour pineapple juice into each mold to fill. Poke fruit with a bamboo skewer or thin knife a few times and tap bottom of mold on counter a few times to release any air bubbles. Place lid on top and insert damp pop sticks. Place mold in freezer and freeze for 8 to 12 hours.
To unmold your pops: Fill the kitchen sink with lukewarm water. Run water over the lid a few times to loosen it. Swish the bottom of the mold through the water 5 or 6 times to loosen the pops. Place the mold on a clean kitchen towel and pull up on the middle sticks to remove all 10 pops and the lid. Swish in water again if all the pops and the lid don't lift off. Then remove the pops from the lid. Store the pops in the freezer in a single layer in ziplock freezer bags.