Louise lost her partner Sean McGrotty (49), sons Evan (8) and Mark (12), mother Ruth Daniels (59), and her 14-year-old sister Jodie-Lee in the tragedy last month.
Their car left Buncrana pier in Co Donegal and entered Lough Swilly.
Baby Rioghnach-Ann was the only survivor after Mr Walsh dived into the water and rescued her from the car before it sank.
A team of friends and family, including Louise and Davitt, are now preparing to run the Belfast Marathon on May 2 as part of #teamEvan.
They are raising funding and awareness for Muscular Dystrophy Duchenne Research Breakthrough Fund as Evan had the condition and had been fitted for his first wheelchair just before his death.
The team is being organised by Thomas McCallion, who is the father of one of Evan's best friends, Tom. He said: "They went to school together and the family live three doors from my mother so they spent a lot of time in school and outside school together.
"In the week of the tragedy, Tom asked me if I would run the Belfast Marathon for Evan. He knew it was coming up and he wanted me to do it in Evan's memory."
Thomas is also running the London Marathon the week before but he agreed to take part in the race for his son and his friend.
Thomas said: "In the past, my kids have run the last bit of the marathon with me so he asked if he could do some of it with me. It's really about him doing something for Evan."
When friends and family heard about what Thomas was doing, they asked if they could help and now they have more than 130 people running.
Thomas said: "We'll have 26 relay teams and each final leg will be run by close family and friends of Louise. That's the significance of it. It's not about any club or anything. It's purely for them.
"I have my own reasons to remember Evan. He spent a lot of time with my family and he was a very clever and witty boy. He never let his condition get to him. #TeamEvan is about remembering such a special boy and the wider family circle. They were a special family and this is a chance for us all to come together to do something."
Louise and Davitt will also be joined by Louise's brother Josh as well as members of Sean's family.
"It's all about the family and we will support them," Thomas said.
"This is their chance to get together in their grief. I think it will be quite a difficult day for everyone because so many people are very close to the situation.
"We're all quite emotional even just chatting about what is going to be involved. Louise is helping behind the scenes and her strength has given everyone the confidence or the will to do this."
The runners will wear orange - the colour of the Muscular Dystrophy charity - and they are working closely with the charity to raise as much money as possible. Thomas said they are also encouraging people to come out and cheer them on as they run the 26.2-mile route.
"We're encouraging people to come out and show their support. I know Louise has appreciated the messages from across the world but this is a chance for people to cheer everyone on along the way."
To donate go to: www.justgiving.com and search for #teamevan