The duo are starring in the 2021 season of Celebrity Apprentice where contestants battle it out to raise money for their charity of choice and the pop duo are honouring their mum with their's.
"I can promise you 16 years in the thick of the music industry means we know how to fight for what we believe in," Lisa shared to Instagram.
"All in the spirit of raising money for our charity of choice @brainfoundation where $ raised goes directly back into research.
"Honouring & raising awareness on behalf our mummy Colleen who is living with a rare neurological condition & who has taught us to be the strong-hearted women we are today."
Lisa and Jess revealed their mother's official diagnosis last year in an Instagram post, where Jess posted a photo of the three of them together in the hospital.
"Our mummy was finally diagnosed with an extremely rare neurological condition called #Progressivesupranuclearpalsy after many misdiagnosis. There is no cure, no treatment, & little to no research, support or funding to do with this disease," she penned.
She added: "We don’t share the reality of this part of our lives. Its private, too confronting, too devastating and almost beyond our human capacity to process the daily grieving and energy required.
"We don’t share any photos or videos of what really goes on behind the smiling photos, but to those who know the reality of terminal illness, our hearts are with you."
True to the testament, the sisters have long kept their personal lives as private as possible, but will occasionally share an update with their fans.
Just last year, Jessica announced she had split from her fiancé Kai Carlton in a post on her Instagram stories.
"To all the souls messaging me about Kai – we are no longer together. I was not afforded any real explanation to address this with clarity here," she said.
"While I appreciate your concern, as much of our relationship was on social media, I don’t know what to say except that I wish to put this behind me, and I’m lucky to have people who love me to support me through this time," she added.
Lisa also shared her own heartbreak with fans, revealing she'd suffered an ectopic pregnancy last year, after she married her long-time partner Logan Huffman in 2018.
In a series of Instagram stories, she explained that she did not want to simply show the "shiny highlight reel of life" but the "shadow and the light, the true human experience."
“Inevitably, I know one day we will have a family. But it just wouldn’t feel right to share the good news in the future, without paying respect, love and bringing awareness to the heartbreaking journey so many women and couples face everyday,” she said.