The first movie Twins came out in 1989. After the success of the film, which highlights noticeably physical differences between two "brothers", Danny DeVito and Arnold Schwarzenegger were asked to return and would have been joined by Roseanne
Barr, who was about as popular a female actor as there was at the time.
It wasn't confirmed, but it is thought that the reason the movie never happened was due to Schwarzenegger turning down the film to prep for Terminator 2, which was probably a wise choice. The studios probably also dodged a bullet with Roseanne who wound up being one of Hollywood's biggest collapses. Still, it was clear why almost everyone wanted to do another film. The first grossed over $216 million worldwide. Not bad for a comedy that on paper probably shouldn't have worked as well as it did.