Investigators were still working to determine the cause of deaths of the three others. The victims were found tangled in a pile of clothes when police went to the home about a child custody dispute Friday.
Marcus Wesson, thought to be the father and grandfather of the victims, walked out of the home covered in blood and was booked on suspicion of nine counts of murder.
Police said Wesson, 57, may have been involved in polygamy and is thought to have fathered children with at least four women, including two of his own daughters.
In a Friday afternoon press conference, Fresno police chief Jerry Dyer said Wesson was cooperating with investigators, but no motive had yet been determined.
Dyer called the slayings one of the worse cases he's ever seen.
"It's just the feeling you get seeing ... people deceased all in close proximity to each other," Dyer told The Fresno Bee.
"Three toddlers and an infant is possibly the most disturbing thing," he said. "No, it is the most disturbing thing."
Dyer said police had been called to the Wesson home six times in the past three years, but never for reasons relating to children or violence.
Wesson's arraignment was scheduled for Wednesday, and bail was set at $9 million.
Authorities expected to complete the autopsies later Monday and release the names of the victims: a 24-year-old woman and eight children ranging in age from 1 to 17.
Coroner Loralee Cervantes told the Fresno Bee that police conducted tests to determine if there was gunshot residue on the hands of one of the victims, indicating Wesson may have had help with the shootings. Police Lt. Herman Silva said that checking for residue is standard practice.
Acquaintances said Wesson and his family appeared to live a nomadic, insular existence. The family moved several times in recent years, from a small boat anchored off Santa Cruz to the mountains outside Watsonville, before settling in Fresno.
In the early 1990s, Wesson lived with a few children on a battered, 26-foot sailboat that had no toilet or bathing facilities.
During that time, he was jailed briefly after being convicted of welfare fraud, the Santa Cruz Sentinel reported. Wesson failed to list his boat as an asset on welfare forms. He also was frequently delinquent with his slip fees, the newspaper said.
Others acquaintances said Wesson appeared with women and children who seemed to be under his control. Frank Muna, a lawyer who once sold the murder suspect a house, said the women wore dark robes and scarves, walked behind Wesson and did not speak when he was present.
The children were home-schooled because Wesson did not trust public education, his sons said, and Wesson, who did not work, was supported by the women.
His sons, Dorian, 29, who lives in Santa Cruz, and Serafino, 19, who lived at the Fresno house, could not say whether he was married or how many children he has fathered, the Fresno Bee reported. They said the family belonged to the Seventh-day Adventist church.