Mother and Son (1984)

Season 5: Episode 7

All Arthur wants is to bring home a girlfriend for Sunday lunch, but convincing Maggie is the trouble. So he disguises his girlfriend as a distant cousin who is visiting the family, and this impresses Maggie, who just loves the family. Arthur gets the whole family together and lets Robert and Liz in on the secret, but they have a hard time keeping it from Maggie when an argument breaks out between Maggie and Liz.