Sophie, who worked in corporate finance and lives in Balfron, near Stirling, said: “It’s quite a prospect, but an exciting and emotional one.
“We are in-training to get ready, but cycling long distances daily and camping each night for weeks is a very different prospect at the age of 62, than it was as 22-year-olds.”
Sophie’s son Hector died from sudden unexpected death in epilepsy (SUDEP).
She said: “More research is needed to identify the causes and ways to prevent SUDEP deaths. Donations will be split evenly between both charities.”
Former BBC journalist Craig Swan, who lives in Grantown on Spey in the Highlands, said like many people all three had been affected by deaths of loved ones.
He added: “Life can be hard. This is an opportunity for all of us to finish what we started 40 years ago, and at the same time help causes very close to our hearts.”
The friends will cycle south along the whole length of a road called Carretera Austral.
They hope to reach Villa O’Higgins, a small town in southern Chile, next month.