Luke and Ryan Hart's determination to get the best grades and the best job was motivated solely by their desperation to free their mother and sister from a lifetime of suffering at the hands of their abusive father.

On 15 July 2016, they did just that.

Taking advantage of their father's absence, they put their escape plan into motion, hiring a removal van, driving to the family home in the Lincolnshire village of Moulton and hurriedly packing up their belongings before fleeing with mum Claire and sister Charlotte to a rented house.

The family were finally liberated from the oppressive regime; free to start a new life together away from a scheming and controlling man they had feared for so long.

Just four days later, Claire and Charlotte Hart were dead.

As they left their local swimming pool in Spalding, Lance Hart crawled from underneath their car, pulled out a single-barreled shotgun and shot his wife and daughter before turning the gun on himself.

"It was my dad who shot me," Charlotte Hart said in her final moments.

Luke and Ryan, both working abroad feeling safe in the knowledge that their mother and sister were safe, received a BBC News alert on their phones.

"I just got back to my desk after lunch and checked my phone and saw a breaking news story saying 'Shooting in Spalding, three people involved'," Ryan recalls.

"At first, I was trying to think it wasn't real or wasn't them or some misunderstanding - but then I called mum and Charlotte and couldn't get through.

"It wasn't until I had a phone call from one of my mum's close colleagues who just said 'Come home mate, come home' and that's when I knew it was them."

The brothers describe the days and weeks that followed as "deafening", with their father's final brutal act generating national and international headlines.

They also discovered that their father had been concocting his murderous plan for weeks - and that they too were his intended victims.

"We found out after that our father had been writing a murder note weeks before we planned to move out and he had been Googling plans to kill his family weeks before that," Luke says.

"So it was cold-hearted and planned and not a snappy decision as is so often portrayed."

On the second anniversary of the tragedy, Luke and Ryan have now made it their "moral obligation" to be a voice for the voiceless, whether that be the fallen victims of domestic abuse or those who are still too terrified to speak out against their perpetrators.

They channelled their grief into writing a book titled 'Operation Lighthouse' - named after the police investigation into their mother and sister's murders - to expose the complexities of domestic abuse through harrowing testimony of their father's abuse.

Luke and Ryan admit they were fooled into thinking that their father's behaviour was not domestic abuse as they believed the "myth" that this was classed as just physical violence.

"We never considered that he would kill us because we never considered how dangerous that controlling mentality actually is," Ryan explains.

Their motivation for speaking out is also fuelled by their wish for their mother and sister's voices to be heard - and not that of their killer father whose 12-page murder note attracted so much media coverage in the days after the shootings.

"Often in domestic homicide, the women and children are murdered and silenced and never get a chance to speak, and it's always a letter or murder note left by the male murderer," Luke says.

"As two young men who grew up under that, our book is an antidote to the murder notes of the men - our book is a victim's note and men giving voice to the victims, particularly our mum and sister."

He adds: "Like the note that was never left."

They describe their mother and sister as "the most selfless people you could ever imagine to meet".

Claire, who worked at the local Morrison's, decided to learn sign language so a deaf customer could feel at ease in the store. Charlotte inherited her mother's kindness, regularly volunteering with the elderly and disabled.

"They were sort of the antidote to our father; our father was all about taking and my mum and sister were all about giving," Luke says.

"They taught us that even in an environment full of hate, it doesn't have to infect you - it is possible to love."

As his kind-hearted children and wife grew closer, an increasingly paranoid Lance Hart continued to foster a climate of fear in the family home.

"There were no physical scars or wounds but he had ways to scare us or force us into submission," Ryan says.

"Our father used our love against us."

He would withhold money to effectively force his wife and children into poverty, blame them for the financial woes that he had caused and retaliate if he believed conversations were happening inside the house without him present.

"We couldn't leave the living room as our father would follow us around the house - he would even break into the toilets to see where we were."

The brothers recalled one disturbing example where their father deliberately fed a then three-year-old Luke peanut butter, despite knowing he had a severe nut allergy.

This was motivated, they say, by a desire to make it explicitly clear that he was in control of all of their lives.

"He created the conditions to be seen as our saviour when he was in fact the abuser," Luke says.

They have spent the past two years re-analysing their early years, comparing stories and gradually accepting that the life they thought they knew was built on their father's lies and games.

"Our father was the only father we ever knew - so most of our lives we thought it was normal for families to live like that," Ryan says.

Luke adds: "How we lived wasn't how it was - it's as if our entire life at this point has been a film or a game - it doesn't feel like we have been really living."

Unwilling to let the unimaginable horror define them, the brothers have vowed to channel their pain and grief to save women and children like Claire and Charlotte.

"What keeps me going is we can live through the love that they gave us, we can share their meaning, their story, their message - if it wasn't for them we wouldn't have got through the last two years," Ryan says.

"We have created a book to not only help others but it's our mum and sister's legacy."

Smiling at the fond memories of his mother and sister, Luke said: "It feels like we are making them proud. It's like they are watching - or we like to think they are.

"The closer we can be to their ideals, the more we feel like they are still here."