Barrass and Machin tried to kill six of their children over a horrifying 48-hour period. As well as trying to poison Tristan and Blake before strangling them, an attempt to drown another child failed.
Sheffield Crown Court heard how Barrass strangled Tristan with her dressing gown cord while Machin strangled Blake with his hands. They then suffocated them by putting plastic bags over the boys' heads.
Tristan and Blake were found by paramedics in a critical condition at their home at 7:30am on May 24 and taken into hospital, but they later died just 12 minutes apart.
Barrass' four other children, who can't be named for legal reasons and are all under the age of 13, were taken into hospital but released the same day.
One of the kids who survived social workers they were 'worried they would become a murderer when they were older because that is what his mum and Brandon did.'
Machin and Barrass are from a dysfunctional family and Machin put himself in the care system as a teenager. The court heard that when he was released he began a sexual relationship with his half-sister Sarah Barrass.
Prior to the murders they were in a secret relationship, with barrister Kama Melly QC telling the court: '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... 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.'
Bryan Cox QC, mitigating for Barrass, said she was 'profoundly damaged by her childhood'.
They were both jailed for a minimum of 35 years and won't become eligible for parole until they're in their seventies.