Michael Griffiths, Adam Holt, Tom Smith, Sam Nicholls, all of Hornby, will be guided by their good friend and expert climber David Redhead, of Ingleton, to trek up Whernside, Ingleborough and Pen-y-ghent.
They were inspired to take on the challenge, know as the Yorkshire Three Peaks, as they have known family and friends use the Preston-based centre for treatment.
Read about previous challenges: Boys from New Longton Scouts complete Yorkshire Three Peaks for Ugandan community and Catterall fund-raisers lead an army for The Matthew Hesmondhalgh Memorial Fund in GarstangSam, 29, said: “We have all had family and friends who have benefitted from Rosemere and their treatment has been successful.
“It is such an important foundation. It is reliant on donations and if it was to disappear it would have a huge effect on people - more than they would realise.
“We decided to challenge ourselves to raise money. None of us are keen outdoor walkers and it is not something we have done before.
“But we are being guided by our friend David who has climbed the Three Peaks before.
“We have started training and climbed Ingleborough in 50mph winds and torrential rain, so I hope that doesn’t happen when we do the challenge.”
The group will do the Yorkshire Three Peaks on March 10.
To help them reach their target of £3,000, visit www.justgiving.com/fundraising/sam-nicholls5