It Takes Two (1995)

Plot
Two unrelated young girls who happen to look identical suddenly meet. Amanda Lemmon (Mary-Kate Olsen) is an orphan, and she is about to be adopted by the Butkises, a family whom she doesn't like. She actually wants her child-loving social worker, Diane Barrows (Kirstie Alley), to adopt her instead. Diane would like to do so, but authorities will not let her because of her low salary. Alyssa Callaway (Ashley Olsen) is coming home from her school's piano recital competition, only to find that her wealthy father, Roger (Steve Guttenberg), is about to marry Clarice Kensington (Jane Sibbett) a socialite who threatens to send her soon-to-be stepdaughter to boarding school in Tibet.

The girls switch places and find out that Roger and Diane would fit together perfectly. So they arrange "chance" meetings with the desired result: they fall in love with each other. After some turbulence, Alyssa (who poses as Amanda) ends up being adopted by the Butkises. She and Diane (while looking for Alyssa) find out the only reason they have adopted so many kids was for them to work in their salvage yard.

When Clarice secretly spies on Roger and Diane, she decides to move up the wedding from the next month to the next day. Roughly two hours before it, Amanda, who poses as Alyssa, proves to the family butler, Vincenzo (Philip Bosco), who she really is. He summons to have the real Alyssa picked up from the Butkises' salvage yard to stall the wedding. Once she and Diane show up, Roger stops it and tells Clarice that he fell in love with Diane. Furious, she slaps him and prepares to do the same to both Amanda and Alyssa but is stopped by both Vincenzo and Diane. She storms out, embarrassed. Alyssa embarrasses her even more by stepping on her gown, causing the skirt to rip off, revealing her white underpants and stockings in front of everybody, including people with cameras. Roger and Diane both find out in the end that it was Amanda and Alyssa that arranged all the meetings between both of them the entire time but it ends happily.