The pair, who are now both 15 and cannot be named for legal reasons, were told they will serve a minimum of 20 years in jail when they were sentenced at Nottingham Crown Court.
The bodies of Mrs Edwards and her daughter were discovered at their home in Dawson Avenue in Spalding, Lincolnshire, on 15 April.
The court was earlier told that the boy and girl - who are believed to be Britain's youngest double murderers - plotted the "rational, logical and cold" murders over several days.
They carried out their plan "almost to the letter" to stab both victims through the voice box so they would be unable to cry out.
Sentencing the pair, Mr Justice Haddon-Cave said: "This case is, in many respects, without parallel.
"This is a case of double murder. One of the victims was a young girl. There is a clear intention to kill both victims - both defendants admitted wanting to murder them.
"There was remarkable premeditation and planning - it was, on any view, substantial, meticulous and repeated.
"The killings were brutal in the form of executions and both victims, particularly Elizabeth Edwards, must have suffered terribly in the last minutes of their lives."
Eight sharp force injuries were found by a pathologist on Elizabeth Edwards' body, of which five were on her hands, suggesting "she may have been trying to fend off her killer".
Her daughter was found with two stab wounds to her neck and a pillow over her face.
A post-mortem examination concluded she died from bleeding and "smothering".
Officers found the murder weapon, a 20cm kitchen knife, discarded on a chest of drawers in the 13 year old's bedroom.
After the murders the teenagers shared a bath, drank alcohol, had sex, and watched Twilight movies.
The girl told psychiatrists that she had "felt like murdering for quite a while", and had held a grudge against Mrs Edwards.
When asked how she had felt about the killings in her police interview the girl said: "I was OK with it. Just the fact that it happened so quickly gave me peace of mind."
Jane Blandford was friends with Elizabeth Edwards who she described as "funny and lovely" and "still missed".
DCI Martin Holvey, from the East Midlands Major Crime Unit, said the details of the case were horrific.
"(They were) very cold, lacking of remorse, with no care for anyone else. Very strange individuals.
"Anyone who would commit such a crime as an adult is very rare but for two children, 14-year-old children, to think up such a crime ...it's unprecedented. Certainly both in Lincolnshire and I'm sure nationally."
In October, a jury rejected the girl's argument that she was suffering from "an abnormality of mental function" at the time of the killings and convicted her of murder.
The boy had previously pleaded guilty to murder.
The judge is still to decide whether to lift reporting restrictions preventing the identification of the killers.
In a hearing, he said he would make a "reasoned decision in writing as soon as I am able to."
SKY News.
