Arnold Schwarzenegger has always wanted to do a sequel, called Triplets with Danny DeVito and adding Eddie Murphy as a long lost third brother. DeVito pitched script ideas back in 2003 but Schwarzenegger was too busy running for governor of California. DeVito agreed with his decision but doubted he would become governor. In 2012, at the end of Governor Schwarzenegger's second term, plans for the sequel were officially confirmed, although as of 2019, Triplets is still in pre-production, and in April 2019, DeVito publicly disclosed that the final script is still incomplete.
Universal needed to know if Arnold Schwarzenegger, Danny DeVito and Ivan Reitman were committed very early on because they were under deadline. They made the deal on a napkin at lunch with agents; they signed it and DeVito then had it framed.
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.
Arnold Schwarzenegger had a lot of fun working on the film. The part he had the most fun filming, was when his character drives Vincent's (DeVito's) car into the supermarket parking lot on two wheels. In the close-up shots of Schwarzenegger, his reaction and the looks on his face were genuine.
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.
Arnold Schwarzenegger, Danny DeVito and Ivan Reitman were realistic and levelheaded about business and thought Twins (1988) might be a difficult sell. However, once they began screening the dailies they knew the film would be a hit because the people in the dailies screening room were laughing at six different takes of a scene.
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.
In an interview with the Academy of American Television, Danny DeVito said when he was called to make the film, he asked if the other twin had been hired. As soon as he found out it was Arnold Schwarzenegger, he asked: "The Austrian bodybuilder?" When he was confirmed, Danny said: "I am signing. Nobody will believe I am the twin brother to Arnold Schwarzenegger. "
The second feature film released in 1988 in which Arnold Schwarzenegger stars as a man who goes to the United States and is not familiar and doesn't understand American culture. The other film is Red Heat (1988), in which he portrays a tough Russian cop named Ivan Danko.
The film makes two references to Arnold Schwarzenegger's earlier film The Terminator (1984): Julius says "I'll be back!" when he threatens Traven, plus Julius and Vincent wear matching sunglasses, which are reminiscent of the sunglasses Arnold wore in The Terminator (1984), and in it's sequels. In the The Terminator films, Arnold's Terminator character's catchphrase is "I'll be back!" and The Terminator wears sunglasses.
Granger's (one of the six fathers) grandson is played by Jason Reitman, who would go on to be a successful filmmaker, receiving Best Director Oscar nominations for Juno (2007) and Up in the Air (2009).
When Julius and Vincent pass each other outside the cinema. The marquee outside the Grauman's Chinese Theater lists the film Willow (1988). "Willow" was released in the United States on 20th May 1988. "Twins" was released in the United States on 9th December 1988.
Arnold Schwarzenegger was the original choice for Judge Dredd (1995), but Schwarzenegger's friend and former rival, Sylvester Stallone was cast instead. In the film, Judge Joseph Dredd and his brother and nemesis Rico discover they were both created in a genetic experiment. Julius and Vincent were created in a genetic experiment.
When the film premiered on BBC1 in the UK in the early 1990s, in the scene where Vincent and Julius visit Mitchell Traven, Julius (Arnold) says "For the first time in my life, I am mad!!" and calls Traven a "Slimeball". In the theatrical version, Julius says "For the first time in my life, I am pissed off!!" and calls Traven a "Dickhead".
The film was mentioned by Doug Gottlieb on The Doug Gottlieb Show (2014) (a sports radio show). Gottlieb compared real life twins, Anthony and Antoinette Davis, to the film's stars, Arnold Schwarzenegger and Danny DeVito. Anthony Davis was a 6'10" forward for the University of Kentucky basketball team, and dwarfs his twin sister Antoinette, who checks in at 5'8".
In the scene when Julius and Vincent are walking down the street in matching suits, Vincent calls Julius "Mr. Ice" in reference to how cool he looks. Arnold Schwarzenegger later played Mr. Freeze in Batman & Robin (1997).
When Julius replaces his torn shirt at a gas station halfway to New Mexico, Julius' new t-shirt art depicts 'Born to be Bad', an album and a single released in the same year by George Thorogood, whose single 'Bad to the Bone' was used on the soundtrack for Terminator 2: Judgment Day (1991), also starring Arnold Schwarzenegger.
When Professor Traven shows Julius and Vincent the room that they were "created", there is an Intravenous Vial with clear liquid in it. If hypothetically that room hadn't been used since the Twins were born and there was an intravenous fluid from back then, it would be old and mouldy. And if the room had been used recently, it still serves no purpose being there.
When Julius and Vincent leave the art colony, Vincent throws the bunch of flowers he brought for his mother on the floor, as he had one and Julius had another. However Marnie is holding 2 bunches of flowers and another bunch is on the floor.