Mrs King says it is important to the couple that they are at the roadside as they want to represent their daughter while David and Sergio, who are running in honour of their girls, are cheered towards the finish line.
"They were such wonderful, caring little children," she says. "Even though none of them knew each other, they were all so similar. And I reckon they are just up there watching over us and looking out for us."
Mr Stancombe is raising money for Elsie's Story, a charitable trust that makes grants to assist young people and support others in the Southport area.
"I keep saying Elsie and those other girls will live longer than us," says her mum, Jenni Stancombe. "Elsie's Story and the work that we're doing in the community will continue [her legacy]."
She says the grants are for "causes that will bring joy, happiness and support to children… Elsie wouldn't want it any other way".
Mrs Stancombe says she chokes up at the thought of David crossing the finish line and imagining what their daughter's reaction would have been.
"She'd be shouting from the line, you'd hear her above everybody else," she tells us. "She'd take his medal off him straight away."
Mr Stancombe says around 40 friends and family will be in London to cheer him on, all wearing hoodies and t-shirts featuring the Elsie's Story logo.
"I've seen so many videos of people crying at the end of the London marathon and I can't imagine what that will be like," he says. "But I want to enjoy the day. I want to do it for me and I want to do it for Elsie."
Mrs Stancombe is certain her husband will complete the marathon, having witnessed his resilience and determination during training.
"I have absolutely no doubt, but I know it will be Elsie who'll be the one to carry him over that finish line."
The 26.2 mile (42 km) route finishes on The Mall in central London and, like David, Mr Aguiar is committed to reaching it.
"Twenty-six miles, I've never done anything like that before. But for my girl, I would do 26 or 50 – whatever," he says. "The pain doesn't matter, I'm going to do it."
He is raising money to build a new playground, including a performance stage and library, at Churchtown Primary School, where Alice was a pupil.
It will be dedicated to Alice and Bebe, who previously attended the school.
Alexandra Aguiar, Alice's mum, says her daughter would have loved to see "her friends play on the playground that [bears] her name".
"The fact her name will be overlooking the playground forever, that would make her feel special," she says. "And [I'm sure it's the] same for Bebe."
Mrs King agrees, saying the new playground is a fitting tribute. "It's really special that all [Bebe's] friends from that school will have this lasting legacy of her," she says.
"She'd be over the moon that she could bring some happiness to her friends and the kids of Churchtown."
Ms Aguiar also feels her daughter will be accompanying her dad in spirit during the marathon. "She's always with us. And she's going to be there helping daddy."
She says she knows how Alice would have celebrated his efforts: "She would have made a big thing of it and told everyone. She would also bring her shopping list to do after the marathon!"
Running alongside Mr Aguiar will be Jinnie Payne, the headteacher of Churchtown Primary School.
She says she has been struck by his courage to run and focus on the playground project.
"His determination [and] his resilience give me so much strength," says Ms Payne. The project, she says, is ultimately about Southport remembering the girls.
Mrs Stancombe and Ms Aguiar will be at the marathon to support their husbands. However, both say it will be their daughters – not them – who helps them cross the finish line.
