Dice the lobsters into large pieces and place in a large mixing bowl. Add the onion, tomatoes, scallions, and orange segments.
In a separate bowl, combine the mango nectar, lime juice, and the passion fruit juice. Add the juice mixture to the lobster mixture and season with cilantro, salt, and pepper, to taste.
Arrange sliced mango and grapefruit segments on a plate and top with ceviche.