An allegedly violently mentally ill man allegedly stabbed his mom and his brother’s wife and two kids to death, before stuffing the children into a closet in a bloody scene in Bensonhurst, police and neighbors said Saturday.

NYPD officers found the body of mother Fayzidva Mavlyuda, 56, with multiple knife wounds to her neck, and wrapped in a blanket inside 1590 West 8th St. near Avenue P around 10:20 p.m. Friday, authorities said.

The bodies of the two kids — a girl, Kamila Shavkatova, 5, and a boy, Timur Shavkatov, 4 — were found stabbed and shoved in a laundry bag hidden away in the closet, the sources said.

The alleged killer’s sister-in-law, Maftuna Khakimova, 27, was found nearby with multiple stab wounds.

The 24-year-old — believed to be one of Mavlyuda’s sons and the uncle of the dead children — was taken into custody at the scene, police said. Charges were pending Saturday.

A now guilt-ridden neighbor stood outside the apartment door recording the chaos, capturing the sound of the terrified children screaming “Mama,” and “Mom,” according to audio heard by The Post.

“He keeps saying why didn’t I call the cops? Why didn’t I come to the door?” said the neighbor’s father, who declined to give his name. “But if he would have come to the door, it would be five dead.”

Another neighbor who gave his name only as Paul said he was outside smoking with his friends and saw the alleged killer walk out of the building.

A short time later, the father of the kids followed and asked the smokers, “Have you seen my family?”

“He ran out … and said ‘My mother is on the floor, there is a lot of blood,’ ” the neighbor recalled. “ ‘My family has disappeared.’ ”

The father, who called 911, then went into the apartment with detectives when they arrived.

Meanwhile, the suspect came back, the witness told The Post.

“‘I’m innocent. Arrest me. It wasn’t me,’ ” the suspect screamed, according to Paul.

The suspect could be heard telling police that “someone else was in the apartment,” the neighbor said, before authorities cuffed the screaming man and put him in the back of a police car.

The alleged killer was known in the building and his family didn’t let him out often, Paul said.

“He was scary,” Paul said. “I stayed away from him. He was a big guy, aggressive, with a look in his eyes like a crazed bulldog.”

About a year and a half ago the suspect started telling people to call him “sensei,” said another neighbor who didn’t want to be named.

“You could tell something wasn’t right with him,” she said. “He stopped smiling, stopped saying ‘Hi.’ I asked him if something happened, and he said ‘Yes, something with my dad.’ He didn’t elaborate.”

Another resident of the building heard the violence unfolding.

“I heard someone screaming so I had a feeling, you know, that something bad was happening, somebody got hurt,” said Jennifer Ponzi. “I saw three body bags go out into the coroner’s car.”

Ponzi, 44, recalled seeing the young wife in the neighborhood.

“You would see her in front of the building,” she said, adding, “It’s sad, it’s horrible. Babies shouldn’t die no matter what.”

A neighbor who identified himself as Javo said the alleged killer smoked pot and had graduated to other drugs.

“When he smokes and does other things he can’t control his anger,” the teen said of his neighbor’s pot smoking.

The NYPD didn’t immediately respond to questions about prior incidents at the home.

Additional reporting by Claire Samstag and Dean Balsamini