A woman and her half-brother have been jailed for murdering their two children by strangling them and placing bin bags over their heads - and conspiring to kill four others.
Sarah Barrass and Brandon Machin - her half-brother and the father of all six children of her children - both previously pleaded guilty to the killing of Tristan, 13, and Blake, 14, as well as admitting to conspiracy to murder six of her children, including Tristan and Blake, and five counts of attempted murder.
Mr Justice James Goss handed the pair life sentences with a minimum of 35 years for the murders of the two boys, who they tried to drug before strangling them and covering their heads with bags to 'ensure' they died.
Kama Melly QC, prosecuting, told Sheffield Crown Court the defendants hatched a plan to kill the children because they feared they were going to be taken into care.
Barrass, 35, and Machin, 39, attempted to murder Tristan, Blake and two other children on May 23 by forcing them to take tablets that the pair had gathered from around the house, the court heard.
Barrass then sent messages and made social media posts claiming her children were suffering from a sickness bug.
On the morning of May 24, Barrass searched the internet for alternative ways to kill her children after expecting them to die overnight, the court heard.
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She called Machin and told him the plan had not worked and he needed to come to the house in the Shiregreen area of Sheffield.
The court heard that between 6am and 7am that morning, Barrass strangled Tristan by wrapping her dressing gown cord around his neck and pulling for around three minutes while Machin strangled Blake with his hands.
Miss Melly told the court: "They decided the children were better off dead than in care and [Machin] said he would help Sarah Barrass to the best of his ability.
"Barrass and Machin first strangled Blake, then Tristan, then placed bin bags over their heads to ensure their certain death."
She told the court that Blake saw his mother strangling Tristan with the cord before he was strangled by Machin.
The defendants then ran a bath and repeatedly tried to drown one of the younger children, who survived the ordeal, the court heard.
Following the murders, Barrass took the surviving children into her bedroom and eventually called the police.
She later told officers that she had planned to kill all six of her children and then kill herself.
The court heard that Barrass had requested help with her children from the local authority fearing that they would be put into care.
Miss Melly told the court that Barrass sent a message to a friend which said: "I've thought of every possible solution to this mess. Mass murder, putting them all in care, checking in to the local nut house.
"I love my kids too much to kill them, I can't put them into care for the same reason."
Bryan Cox QC, mitigating for Barrass, described her crimes as "evil and nothing but evil" but said she was "profoundly damaged by her childhood".
He said: "The defendant was desperate to prevent her children being taken into care. She couldn't cope with the prospect of them being removed."
Mr Cox also told the court that Barrass had experienced "a chronically traumatic childhood" and had been subjected to neglect and sexual abuse.
Earlier in the hearing, the court heard how Barrass would regularly threaten her children.
"Visitors to Miss Barrass's house would hear her tell the boys 'I gave you life, I can take it away'," Miss Melly said.
"Speaking to the boys in that way was described as an everyday thing."
The court also heard a victim impact statement put together by social workers, which described how the child who the pair tried to drown 'doesn't like baths anymore' and the remaining children are 'emotionally broken'.
All the surviving children, who cannot be named for legal reasons, are under the age of 13.
Barrass and Machin were both jailed for a minimum of 35 years for murder along with an additional 10 years for the counts of conspiracy to murder and attempted murder to run concurrently.
A reporting restriction that prevented the media from disclosing the relationship between Barrass and Machin was also lifted in court revealing that the pair were step-siblings and the parents of all six children.