Speaking exclusively to ITV News, Dawn Bestwick said jail wasn't good enough for MIck Philpott and that "as a coward" he "deserved to die".
The judge has delayed her sentencing to "reflect further" on the trial Mick and Mairead Philpott and friend Paul Mosley.
Tributes have been paid to five brothers and their sister who died in a fire at their family home in Derby in May last year.
– Judge Mrs Justice Thirlwall
You craved attention, you enjoyed the limelight. You courted publicity. You were and remain the centre of your world and it is plain that you require everyone in your life, but particularly the women to make sure that you remain at the centre of their world.
Your needs and desires took precedence over everything, everyone else, including your children.
You so arranged your life and theirs so that everything was done for the pleasure of Michael Philpott.
Bernadette Duffy, Mairead Philpott's sister, left Nottingham Crown Court without comment following the sentencing.
Dawn Bestwick, Mick Philpott's sister, told reporters waiting outside court that justice had been done for the children and they could now "rest in peace".
Andy Lyons, Paul Mosley's brother-in-law, said: "We don't have an eye for an eye. We're not a Third World country but the sentence is the best that the judge can give and makes England the greatest nation in the world."
The senior investigating officer in the Derby house fire case has released the following statement:
– Detective Superintendent Kate Meynell, derby police
Six innocent children died as a result of the actions of their parents, the very people who should have protected them against danger.
The Philpotts and Paul Mosley showed no regard for the safety of the children and since the fire have shown no remorse for their actions.
They have lied throughout the investigation and court case. There were plenty of opportunities to admit their guilt but they never did and persisted with their denials.
This has been an incredibly tragic case to investigate and today’s sentences bring this difficult inquiry to a close.
Paul Mosley, who was convicted of six separate counts of manslaughter following the deaths of the Philpott children, spoke to the Derby Telegraph two weeks before he was charged, telling "lie after lie in a desperate attempt to distance himself from the horrific crime".
During the interview he denied his role in the fatal fire and complained about how he was being treated by police.
He said: "I was arrested after the fire. They took my clothes, my laptop, everything. Now I just want it all back. I want to get on with the rest of my life. I'm going to my MP. I'm seriously going to take it all the way."
The newspaper said Mosley seemed proud that he was the last person to have seen the Philpott children alive and claimed he was at the house with Mick and Mairead Philpott only hours before the fire started.
He said: "I was there on the night of the fire. I was one of the last people to see the kids alive. I'm the main man, the one everyone wants to talk to. I know someone in London who says the media in China will pay me millions for my story."
Amanda Cousins, the sister of Mick Philpott's former mistress Lisa Willis, has told ITV Daybreak that Mr Philpott 'is a very manipulative person.'
She said: "He really is a nasty character, nothing's good enough for Mick's sentence, he should get life."
Mrs Justice Thirlwall adjourned the case because she wanted more time to consider sentences.
She said she had listened with care during the whole trial and added: "I want to reflect further before moving forward to the sentencing exercise."
Mick Philpott delivered "occasional violence" towards Kim Hill before attempting to kill her. She says Mick broke her fingers and arm.
She tried to break-up with Philpott but he told her: "If I can't have you. No f****** going to have you. You are going to be dead b****."
Kim Hill was resuscitated twice after he tried to kill her and she still suffers from the effects of the multiple stabbing.
The Philpotts and Mosley are back in the dock. The prosecution is outlining antecedent history which includes Mick Philpott's conviction for attempted murder and grievous bodily harm (GBH).