Chynna Phillips, Mackenzie Phillips

Mackenzie Phillips' family members are split over the veracity of her claims that she and her father, the late John Phillips, had an incestuous relationship.

"I knew it was true," Mackenzie's half-sister Chynna Phillips told Us Weekly. "I mean, who in their right mind would make such a claim if it wasn't true?"

"They were both doing drugs together. After long nights of heroin use, she's claiming that she once woke up and that my father was on top of her having sex with her," Chynna said. "Was he actually raping her? I don't know. Do I believe that they had an incestuous relationship and that it went on for 10 years? Yes."

News: Mackenzie Phillips says father, Mamas and the Papas' John Phillips, raped her

Michelle Phillips, John's second wife and Chynna's mother, says she has "every reason to believe [Mackenzie's account is] untrue."

"She told me, then she called me back and said, 'You know I'm joking,'" Michelle Phillips told The Hollywood Reporter, adding that Mackenzie told her entire family in 1997. "I said it wasn't funny. Mackenzie said, 'I guess we have different senses of humor.'"

Michelle acknowledges that John was a bad parent and a drug addict. "But f--- his daughter? If she thinks it's true, why isn't she with a good psychiatrist on a couch? I think it's unconscionable that Oprah would let her do her show," she said, referring to Mackenzie's Wednesday sit-down with the talk show host.

VIDEO: John Phillips sings "California Dreamin'"

Mackenzie has "a lot of mental illness," Michelle said, adding that she believes the actress timed the release of her book to steal thunder away from Chynna's new album. "Mackenzie is jealous of her siblings, who have accomplished a lot and did not become drug addicts."

"I am stunned by Mackenzie's terrible allegations about her father," Genevieve Waite Phillips, John's third wife, said in a statement. "I would often complain to John about her overly familiar attitude towards him, and he would tell me that that was just her way. John was a good man who had the disease of alcoholism and drug addiction. He was incapable, no matter how drunk or drugged he was, of having such a relationship with his own child."

Tamerlane Phillips, John and Genevieve's son, did not say if he believes the actress' claims or not, but noted his family's troubled history.

"My family is and always will be a decrepit bowl of dog urine compared to Nityananda of Ganeshpuri," Tamerlane told the New York Post. "That is how great Nityananda is." The Indian yogi died in 1961. "Worship Nityananda, not the Phillips family. Nityananda can protect you."

VIDEO: Phillips tells Oprah that John shot her up with heroin for the first time

In her new memoir, High on Arrival, Mackenzie details an incestuous affair between her and John, who fronted the 1960s group The Mamas and the Papas. Mackenzie says in Arrival that she first remembered having sex with her father on the eve of her wedding to Jeff Sessler when she was 19. She says she passed out from doing drugs and woke up to find John having sex with her.

Mackenzie Phillips, 49, was born to John Phillips and his first wife, Susan Adams, in 1959. Mackenzie has a brother, Jeffrey, and three half-siblings: Chynna Phillips, John's daughter with Michelle Phillips; and model-actress Bijou Phillips and half-brother Tamerlane, whose mother is Genevieve Waite.