Former Eastenders actress Sian Blake and her two young sons, Zachary and Amon, died as a result of head and neck injuries, police said.
Scotland Yard confirmed they were investigating a triple murder following the discovery of the three bodies which were hidden in the garden of the family home in Kent on Tuesday.
Ms Blake (43), Zachary (8) and Amon (4), have now been formally identified and postmortem examinations have taken place.
Arthur Simpson-Kent, Ms Blake’s former partner, is still being sought by police and is believed to have fled the country to Ghana.
Police sniffer dogs led officers to the bodies at the house in Erith, Kent, where “significant attempts” had been made to conceal them, Scotland Yard said.
Murder detectives helped lead a forensic search of the property on Sunday after being drafted in to assist the borough force.
A missing person’s investigation was launched on December 16th when police visited the home following information from the NSPCC which “expressed concern” about Ms Blake’s health and the family’s relationship with Simpson-Kent.
Detectives said they were aware of claims Mr Simpson-Kent had travelled abroad after pictures obtained by ITV News showed him at Kotoka Airport in Accra, Ghana.
Ms Blake’s sister Ava said Mr Simpson-Kent will have to “answer to God” for his alleged actions.
Speaking at Scotland Yard, she said: “Unfortunately I believe Arthur was responsible for my sister and my (nephews’) deaths.
“I want him to face justice and explain why. It’s my nephews more than anything.
“My brother is angry. My cousins are angry and it’s because of the boys.
“They are angry about Sian, but the boys have devastated us. We have lost a generation. We can never replace them.
“I want him to be brought back to justice. He’ll have to answer to the courts of this land and to God eventually. I don’t know what is going through his mind.”
Ms Blake had motor neurone disease - a fatal, rapidly progressing illness which affects the brain and spinal cord - and was reportedly looking “very frail” before she vanished.
She was last seen with her sons in Waltham Forest, east London, on December 13 and officers spoke to Simpson-Kent three days later at the family home in Pembroke Road, Erith.
Ms Blake, who played soul singer Frankie in Eastenders, appeared in the BBC soap for 56 episodes between 1996 and 1997, reportedly quitting because of hostility from viewers towards her manipulative character.