In particular, it was difficult for the family to see camcorder video, shot by a family friend, of a sore-covered Cobain — high to the point that he is nodding off — holding his baby daughter while Ms. Love tries to cut her hair. “I think that they just wish that the heroin wasn’t there,” Mr. Morgen said. “And so do I.”

Ms. Love had no creative input, Mr. Morgen said, but Frances Cobain, 22, served as an executive producer. Ms. Cobain has held rights to her father’s name and likeness since 2010 as part of a confidential agreement with her mother. Ms. Cobain and Ms. Love have a volatile history, with Ms. Love most recently losing custody of her daughter in 2009.

Image Frances Cobain with her mother, Ms. Love, at the film’s premiere at the Sundance Film Festival in January. Credit... Chris Pizzello/Invision, via Associated Press

“Frances wanted an emphasis on the art,” Mr. Morgen said. “She felt that Kurt had been heavily mythologized, and that it was essential to her that he was humanized in the film. It happened that her take was exactly in sync with mine.”

“Montage of Heck,” named for a mixtape Cobain made in 1988, has been greeted with universal acclaim on the festival circuit. The family also seems pleased. “I love it,” said Ms. Love, who receives a fair amount of humanizing in the film herself. “It’s as honest as it’s ever going to get.” Ms. Cobain declined to comment. In an interview with Rolling Stone, she said, “It’s the closest thing to having Kurt tell his own story in his own words — by his own aesthetic, his own perception of the world.”