Luke and Ryan Hart’s mother, Claire, and sister, Charlotte, 19, were shot by Lance Hart in a car park in Spalding in Lincolnshire in 2016. He then killed himself.
The shootings came five days after they had rented a new home for their mother and sister – an “escape plan” they had worked for years towards.
The brothers have since set up the Coco Awareness charity and are speaking at events about how “horribly normal” controlling behaviour is – and how it can prove to be lethal.
The pair told a conference in Hull that the first time they heard of “coercive control” – acts of assault or threats used to harm, punish or frighten a victim – was on a poster in a police station two days after the murders.
“It articulated what we had lived with every day for 25 years,” said Luke.
Their father controlled their lives, especially their mother, a supermarket worker, rationing her meagre earnings, checking receipts and guilt-tripping her over minor purchases.
But he treated himself to holidays, and when she revealed she had cancer he launched a selfish tirade about the stress he was suffering.
He would often call his sons stupid, lazy or useless.
Luke said: "When my mother invited friends around for coffee, father would follow them and listen to them intently. It was simply easier if no one ever came again.
"He never permitted her any freedom, he didn't allow her to have social media or use the Internet. He'd turn up at work to check she was where she should be."
He added: “We never realised it was domestic abuse because our father was never exceptionally violent.
“It was all about him having control. Most women are killed by intimate partners – most men are killed by strangers.
“We saw him as protecting us, keeping us safe from a dangerous world, unfortunately it was all part of a strategy. Murder was the ultimate act of control.”
Ryan Hart said “male entitlement” needs to be challenged and the next generation needs to be brought up with a different set of beliefs, adding: “That they do not feel entitled to own and control a woman and the family.
"Instead that they recognise relationships are about equality and respect.”
After the murder, the brothers had to witness a slew of positive reporting towards their father, suggestions that the prospect of divorce “drove” him to the killings or that mental health issues were at play.
In fact, there was no breakdown, and he was functioning as “he always had”.
Ryan Hart said: “It became clear to us that society considers men’s feelings vastly more important than the lives of women and children.
"It was still possible to be a ‘good man’ – even after murdering his family.
"We had to read of my father's 'suicide note'. My mum and Charlotte would have called it a murder note.
"He'd been writing the murder note for weeks and made online searches about men murdering their families for months."
Vicki Paddison is Strategic Domestic Abuse Services Manager for Hull, where 800-900 calls are made to police every month over domestic abuse.
She said: "Women are seen as home makers, mothers and wives. We are still a million miles away (from achieving equality)
"If you ask a group of 40 women how many spent the weekend washing up and making meals three-quarters will say it's me and my husband helped. We still live in an age with very stereotypical rules and where you have a perpetrator who believes in old-fashioned values, they will use that to kill them."
She said the Media reinforced stereotypes by looking for something negative in the victim that excuses the attacker.
"All the negative stereotypes get assigned to the victim and the positives in terms of excusing the behaviour - mental health, unemployment, stress - are attributed to the perpetrator - I see it time and time again."
Anyone who wants advice or help can contact:
· Hull Domestic Abuse Partnership on 01482 318 759 or www.hulldap.co.uk
· Preston Road Women’s Centre on 01482 790 310
· Hull Women’s Aid on 01482 446099, or
· Strength to Change on 01482 613 403 or www.hullstrengthtochange.org