A woman who murdered her two eldest children and plotted to kill the other four was seen by professionals involved with the family as “a loving, caring and competent mother”, a serious case review (SCR) has found.

Incestuous couple Sarah Barrass, 35, and her half-brother Brandon Machin, 39, were jailed for life last year with a minimum term of 35 years for the murder of 13-year-old Tristan Barrass and his 14-year-old brother Blake, at their home in the Shiregreen area of Sheffield.

On Friday, an SCR found that none of the practitioners or agencies who had contact with Barrass and her children could have predicted what happened.

The report, published on Friday, concluded: “The deaths of these two children is a tragedy and there is no evidence from this review process that any of the practitioners and agencies involved with the family could have predicted the actions taken by their parents.

“This review has seen significant evidence of effective and caring practice with the children by all agencies involved with the family.”

The review said: “Practitioners saw (Barrass) as a loving, caring and competent mother.”

Sheffield Crown Court heard last year that Barrass and Machin worked together to strangle the two teenagers before ensuring their deaths by placing bin bags over their heads.

The court heard that two of the children they had plotted to murder were under the age of three.

The family had contact with a large number of staff and a variety of agencies but the SCR said: “Professionals’ view of mother’s parenting was overwhelmingly positive and she was seen as a competent, caring and articulate parent who supported and fought hard for her children’s access to appropriate support and help.

“She frequently self-referred to support services and the police.”

When the pair were sentenced, the court heard how, a day before murdering Tristan and Blake on May 24 2019, they had also forced the two teenagers, as well as two more of their children, to take tablets gathered from around the family home.

The court that Barrass and Machin expected the mixture, which included prescribed ADHD medication, to kill all four of them.

When that failed, they killed Tristan and Blake before attempting to drown another child in the bath.

Prosecutors said the picture of the family before 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”.

But none of the professionals working with the family knew that Barrass and Machin were in a relationship and that he was the father of all six children.

The court heard: “The children believed and even told officers at the scene that their father was dead, having died in the Second World War.”

A judge was told that the mother-of-six was heard repeatedly making remarks such as “I gave you life, I can take it away” to the children.

The court heard that she had sought help from the local authority with the youngsters, texting a friend: “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.”

The SCR described how social services and other agencies had been involved with the family for many years, with much of the focus on difficulties being faced by a number of the children and particularly troubling behaviour exhibited by the eldest.

Here was a mother who had children with a number of complex and difficult needs, who was asking for help, was accepting and working with the help she was offered in a very constructive and positive way

In prison, Barrass told the report author, Alex Walters, that she feared she was “raising monsters”.

The review said: “The social worker explained and provided assurance on many occasions that the involvement of Children’s Social Care did not mean removal of the children but when asked by the independent reviewer (Barrass) stated that she just could not believe this and was adamant that the children would be removed and placed in care.”

Ms Walters was asked at a press conference whether Barrass had shown any remorse.

She said: “That wasn’t the focus of my discussion with either parent.”

The report, which set out recommendations in seven different areas, described how both Barrass and Machin were asked in prison for their views on the support given to them by agencies.

It said: “As with (Barrass), the focus for the discussion was on the agencies that had worked with the family, what services (Machin) had found helpful, less helpful and what could be improved.”

David Ashcroft, chairman of Sheffield Children’s Safeguarding Partnership, told the press conference he did not accept that the couple “pulled the wool over the eyes” of professionals nor that the children were “failed by the system”.

He said: “Here was a mother who had children with a number of complex and difficult needs, who was asking for help, was accepting and working with the help she was offered in a very constructive and positive way.

“And when she was appropriately and frequently asked about the issue of the parentage of her children, declined to give any information.”

He said that if professionals had know that Machin was the children’s father, it would not have meant they would automatically have been removed from the family but would have fed into the more general child protection picture.