The jury in the Clydach murder retrial has been told it must consider the possibility that one of the girls tried to save their mother from the attacker.
David Morris denies the "massacre" of Mandy Power and her family
Mandy Power, daughters Katie and Emily and their grandmother Doris Dawson were beaten to death in June 1999.
Continuing his summing up, the judge said "words could not convey" the severity of their injuries.
David Morris, 44, from Craig-cefn-Parc, denies the murders at the retrial at Newport Crown Court which began in May.
Summing up on Friday to an almost silent courtroom, the judge, Mr Justice McKinnon, catalogued the horrific injuries to the victims to the jury.
"Words cannot convey the severity of the injuries inflicted upon them," he said.
Ms Power, 34, her two daughters Katie, 10, and Emily, eight, had been battered repeatedly with a fibreglass pole -- their skulls had effectively been smashed, said the judge.
"The pole is 4ft, weighs around 1kg, made of fibreglass, with plastic-like coating," he said.
"The children were aware of the presence of the pole in the house. You've heard from a witness Louise Pugh, that Emily used to play with it."
Doris Dawson, 80, the children's disabled grandmother, had been killed as she lay in her bed before fires were lit to try to conceal the crime.
The judge reminded the jury of forensic evidence which showed the killer had tried to strangle Mandy Power.
"Was that, he said, the first act of violence? Was it then that one of her children got the pole in an attempt to save the life of their mother, a pole they used to play with but a pole that was used to kill them all? "
On Thursday, in his summing up, the judge told the jury they had probably seen the killer of three generations of one family in the court room.
Alison Lewis was the lesbian lover of one of the victims
Mr Justice McKinnon began his summing up by telling the jury: "These were truly terrible crimes that had been committed.
"That three generations of the same family had been savagely battered to death in their own homes."
He said: "You'd need hearts of stone not to be affected by the photographs of the injuries."
But he told jurors they had to "decide the case on the evidence".
Mr Justice McKinnon said the prosecution claimed David Morris, was responsible for the murders while "fuelled by drink and drugs... He committed the worst kind of massacre and sought to destroy the evidence."
But he also said the defence claimed Mr Morris was elsewhere and "they suggest the police had probably got it right in July 2000 when Alison Lewis was arrested on suspicion of murder... perhaps assisted by Stephen Lewis".
The jury were told that in the absence of an unknown intruder "you have seen the killer in that witness box - either David Morris, Alison Lewis or Stephen Lewis".
The jury is expected to retire on Monday to consider its verdict.