A couple in an incestuous relationship who murdered their two teenage sons and tried to kill their remaining four children have been jailed for life.

Sarah Barrass, 35, and her partner, Brandon Machin, 39, who is also her half-brother, planned to kill their six children amid fears they would be taken into care. They were both sentenced on Tuesday to life in prison with a minimum term of 35 years.

Tristan and Blake Barrass, aged 13 and 14 respectively, died after being strangled by the pair at a property in the Shiregreen area of Sheffield on 24 May.

Photo issued by South Yorkshire Police of Tristan and Blake Barrass, aged 13 and 14. Photograph: South Yorkshire Police/PA

A court heard that, prior to the killings, Barrass and Machin had given their four eldest “terrified” children tablets used to treat ADHD against their will. When the tablets did not work, Barrass – who declared: “I gave them life. I can take it away” – searched online for other ways to kill her children, including suffocation, strangulation and drowning.

The court was told Barrass then strangled Tristan with her dressing gown cord and Machin then strangled Blake with his hands.

The pair also tried to kill one of the younger children by attempting to drown them in a bath.

Barrass and Machin had each admitted two counts of murder, conspiracy to murder six children, and five counts of attempted murder.

In sentencing, Mr Justice Goss told Barrass: “You considered [that] your love for them and fear of being parted from them entitled you to take their lives as well as your own.”

The prosecutor, Kama Melly, told Sheffield crown court that Machin was Barrass’s half-brother – both had the same mother – but the pair had a sexual relationship.

She said: “The six children lived alone with their mother, Sarah Barrass. The picture of the Sarah Barrass household prior to the events in 2019 was, to the outside world, a household of a loving single mum with six children, heavily supported by her brother Brandon Machin.

“In fact, unbeknown to everyone but the defendants, Brandon Machin was in a sexual relationship with his half-sister Sarah Barrass, and he was the father of all six children.

“The children believed and even told officers at the scene that their father was dead, having died in the second world war.”

On 23 May, the defendants gathered tablets from around Barrass’s home and divided them among the four eldest children, expecting them to die.

“None of the children wanted to take the tablets but were forced to do so,” she said.

The court heard that Barrass sent messages and made “light-hearted” social media posts overnight claiming that the children had a sickness bug.

Melly added: “They decided the children were better off dead than in care.” After strangling the boys, the pair then “placed bin bags over their heads to ensure their certain death”.

After the murders and the attempted murder of the younger child who was placed in a bath, the mother took the surviving children, who are all under 13, to the bedroom and phoned the police.

Melly said: “Nothing could have prepared those two police constables for the scene they had found.

“The officers found Sarah Barrass barricaded in a room with the four surviving children. She lied to the officers, telling them that her two other children were with neighbours.

“However whilst she was saying this to police, one of the children motioned to the police officer that in fact the children were dead – he moved his hand across his throat. Sarah Barrass told the child to stop what he was doing and stated: ‘Stop, don’t say that.’”

Despite vomiting and having hallucinations, the younger children survived the attempt to kill them and recovered in intensive care. The two youngest surviving children were under three.

The court heard how Barrass had asked the local authority for help with the children, and had texted a friend to say: “I’ve thought of every possible solution to this mess. Mass murder, putting them all in care, checking into the local nut house.

“I love my kids too much to kill them. I can’t put them into care for the same reason.”

In her defence, Bryan Cox QC admitted Barrass’s crimes were “nothing but evil”, but added that she was “profoundly damaged by her childhood”.

The court was told that Barrass had grown up in a home where she had suffered neglect and emotional, physical and sexual abuse, eventually being taken into care.