Arrange oranges, kiwifruit, pineapple, apples, and pears on a large platter; brush with 2 Tbsp. of lemon juice.
Thread grapes on appetizer skewers, alternating colors. Add skewers to platter. Add pomegranate seeds (if using).
For dip, in a small bowl stir together mascarpone cheese, maple syrup, and remaining 1 Tbsp. lemon juice. Serve dip with fruit.
Cover and chill kabobs and dip up to 8 hours before serving.