Sacheen Littlefeather, the activist who famously stood in for Marlon Brando to refuse the best actor Oscar in 1973, faked Native American ancestry, her family have said.

In an article in the San Francisco Chronicle, Littlefeather’s sisters Rosalind Cruz and Trudy Orlandi said that their sister’s claim to have Apache and Yaqui ancestry through her father was “a lie” and “a fantasy”.

Orlandi told the Chronicle: “It’s a lie. My father was who he was. His family came from Mexico. And my dad was born in Oxnard [California].” Cruz added: “It is a fraud. It’s disgusting to the heritage of the tribal people. And it’s just … insulting to my parents.”

Littlefeather died in October shortly after receiving a formal apology from the Academy of Motion Picture Arts and Sciences (Ampas), the body who organises the Oscars, for the way she was treated at the 1973 ceremony. Littlefeather responded at the time with a statement saying: “Regarding the Academy’s apology to me, we Indians are very patient people – it’s only been 50 years! We need to keep our sense of humour about this at all times. It’s our method of survival.”

However, the article’s author Jacqueline Keeler reports that Littlefeather’s birth name was Marie Louise Cruz, and that she has found no evidence of any connection or claim that her father, Manuel Ybarra Cruz, had to Native American ancestry.

Cruz and Orlandi also refuted Littlefeather’s claims of childhood poverty and parental abuse. Cruz said: “My father was deaf and he had lost his hearing at nine years old through meningitis. He was born into poverty. His father, George Cruz, was an alcoholic who was violent and used to beat him. And he was passed to foster homes and family. But my sister Sacheen took what happened to him.”

“The best way that I could think of summing up my sister is that she created a fantasy. She lived in a fantasy, and she died in a fantasy.”

Orlandi added: “My father’s father, George, he was the alcoholic. My dad never drank. My dad never smoked. And you know, she also blasted him and said my father was mentally ill. My father was not mentally ill.

“Sacheen did not like herself. She didn’t like being Mexican. So, yes, it was better for her that way to play someone else.”