The Addams Family (1991)

Con artists plan to fleece an eccentric family using an accomplice who claims to be their long-lost uncle. Gomez Addams laments the 25-year absence of his brother Fester, who disappeared after the two had a falling-out. Gomez's lawyer Tully proposes that Gordon, who closely resembles Fester, pose as him to infiltrate the Addams household and find their hidden vault. As Gordon grows closer to the Addams family, he begins to question his deception but ultimately turns against the con artists to protect his newfound family. In the end, it is revealed that Gordon is actually Fester who had suffered amnesia after being lost in the Bermuda Triangle.