On 22 October 2014, the boys were on an unsupervised access visit to their father, Darren Sykes. The family court had sanctioned the visit despite evidence that Sykes had abused his wife and children. Sykes started a fire in his home while the boys were in the attic looking at a train set, then locked them in. Paul died that same night. Jack passed away a few days later, believing he had saved his brother's life.
Mrs Throssell, from Penistone near Barnsley, spent 12 years campaigning to change the law governing such access arrangements. This week, she saw the Courts and Tribunals Bill go through its final Commons stages, which will remove the presumption of parental involvement from the family justice system.
"Law change will be my sons' legacy. I hope they're proud of me," Mrs Throssell told the BBC, reflecting on the end of a more than a decade-long fight.