The Nutt House (1992)

Identical twins Philbert and Nathan are too much of a burden on their mother, so she separates them by sending Nathan, the "bad seed", to an insane asylum where he grows up with multiple personalities, while Philbert becomes a well-known senator. On a typical day, Nathan escapes from the asylum to find his long-lost brother and somehow ends up at Philbert's mansion, and since they look just alike, they cause outrageously silly mishaps as they fool Philbert's long-suffering wife Diane and his mistress/housekeeper Miss Tress.