Ex-EastEnders actress Sian Blake was about to leave her "controlling" boyfriend before she went missing, her sister has said.
The bodies of Ms Blake and her two young sons, Zachary, eight, and Amon, four, were discovered in the family's home in Erith, Kent.
Police are treating their deaths as murder.
Detectives are urgently looking for Ms Blake's partner Arthur Simpson-Kent who has since travelled to Ghana.
It has now emerged that a relative of Ms Blake contacted the NSPCC on December 16 expressing concerns about domestic violence and the information was passed on to the Metropolitan Police and Bexley Council in London on the same day.
In a tearful interview, Ava Blake said that the couple's relationship "had come to end" and accused Simpson-Kent of being a "controlling" influence who monitored her sister's phone calls.
She said the deaths of her sister and nephews have "devastated" the family, adding: "We have lost a generation - we can never replace them."
Ms Blake, 51, said her sister was "not the vivacious, happy person she once was" in the past year.
Her sister had told their mother, Pansy, that she wanted to get out of her relationship "a long time ago", she said.
She also claimed that texts sent by the actress after she disappeared had not been written by her.
"The ones that came through were very poor grammatically, bad spelling, not my sister."
Miss Blake said the texts alleged to be from her sister said she was going away "for a few weeks", then it became "a few months".
"No way," she said. "We're a big family and very, very close. She would never say that. She would never not speak to us."
It emerged on Thursday that Scotland Yard had been told about concerns over the relationship between Ms Blake and Simpson-Kent on December 16.
A missing person's investigation was launched on the same day after police visited the home.
Ms Blake, 43, had motor neurone disease - a fatal, rapidly progressing illness which affects the brain and spinal cord.
She played soul singer Frankie in EastEnders, appearing in the BBC soap for 56 episodes between 1996 and 1997.
She reportedly quit due to hostility from fans towards her character.