The money was not available to pay to the two main stars and the director their normal fees. They decided to split a percentage of the gross profits between the three of them and ended up making more than they would have made taking their fees upfront because the film was such a hit.
Throughout the movie, Julius tells everyone he meets that he is from an island (shown at the beginning of the movie) in the South Pacific 300 nautical miles (350 miles) SSW of the Fiji Islands. Although the island depicted in the movie is fictional, there is indeed a VERY small island 350 miles in the SW/SSW direction of Fiji known locally as Ceva-I-Ra. Ceva-I-Ra (also known as Conway Reef) is an atoll-type coral reef stretching just under 2 miles long with a tiny sand cay (with some vegetation) in the center approx. 2 hectares in area.
When Julius goes to his mother's old house and meets up with Granger (one of his and Vincent's six fathers), Granger's grandchildren are played by Jason Reitman and Catherine Reitman -- the real-life children of director Ivan Reitman.
Arnold Schwarzenegger, Danny DeVito and Ivan Reitman were all realistic and levelheaded about business and thought Twins might be a difficult sell. But when watching the dailies they knew the film was a hit after people laughed at six takes of a scene.