The title Trouble in Paradise is an indication of the mythic images each character should be associated with. They're the trouble-makers from the fall of man, when Adam and Eve stole the forbidden fruit from God himself, earning themselves a tremendous deal of suffering, but even though their actions are wrong, God lets them stay together for life. That's actually pretty close to the plot of the film.
In the story, Lily and Gaston are lovers and friends, but mostly, they are co-conspirators against the wealthy. Their thievery unites them as lovers, and their constant desire for more makes them hurt each other frequently, but in the end, their love wins, and they make out with all the cash too.
Because the story is a romance, it also has allegorical elements, such as the evaluation of romantic love, and the constant pain the lovers inflict on each other through lies and betrayals. In a way, it's an anti-love story, because the characters are anti-heroes, so their actions are not condoned necessarily, but rather, they represent each person's selfish interests, and the central theme of the story is that love can be betrayed by selfish goals.
