A shattered Sydney community has farewelled a mother and her two young boys after they were killed in an alleged triple murder last month. 

Police found the bodies of Kamrun Nahar, 46, Ayman, 12, and Ayaash, 4, inside their Campbelltown home in the city's south-west on May 18.

Md Shomon Ahamed, 47, was arrested and later charged with their murders. 

Police allege Ahamed planned the crimes after reading reports about a murder-suicide in Perth in January.

Ms Nahar and her sons were buried together in one grave during an emotional service on May 29, 7News reports.

The heartbroken family paid tribute to Ms Nahar as a devoted mother. 

Among the mourners were Ms Nahar's colleagues, classmates of Ayman who studied at a performing arts high school and Ms Nahar's brother Mohammad who travelled from Bangladesh to attend.

Local organisations banded together to ensure the family 'could afford what was required', Catholic Cemeteries' Michael Cashin said.

According to police documents obtained by the Daily Mail, Ms Nahar and her children were stabbed to death. 

Police allege Ahamed used a knife to kill them before phoning triple-zero. 

'They are all downstairs,' he allegedly told the operator, according to the documents.

He allegedly added that the knife was in the garage.

When police entered the home, they allegedly found Ahamed waiting by the door, with Ms Nahar's body in the garage beside a bloodstained knife.

The boys' bodies were found in a bedroom. All had lacerations and other 'significant' injuries. Ahamed told attending officers the boys had autism.

He allegedly said he had struggled with depression since being diagnosed with cancer, which is now in remission.

Ahamed did not appear in court when his matter was briefly mentioned in Campbelltown Local Court last month.

He did not apply for bail and the case was adjourned to July 15. 

The alleged murders have left residents in the usually quiet neighbourhood reeling. 

Amanda Wasillewski, who lives three doors down from the family's home, said she had only met the alleged victims once.

'It was a chance meeting - our peacock flew into their yard, so I had to go over and catch her and I met the two children,' she told the Daily Mail.

She said locals often referred to the neighbourhood as 'the retirement village' because of how quiet it usually was.

'We didn't hear anything - not even a peep, because normally we would be alerted if we heard a scream or anything,' she said.

'We would have gone to investigate to see if someone needed assistance, but there was absolutely nothing.'

Another neighbour was seen placing roses outside the home. 

'This is just terrible to wake up to find out this happened on my mother's street, I can't believe it,' they said.

'I'm feeling for these children, their friends, they've gotta go to school and find out their little mates aren't coming to school today - it just breaks my heart.'