Colin Coats and Philip Wade (both 42) were found guilty as the other two – David Parker (38) and Paul Smith (47) – had guilty pleas for reduced charges of assault on Ms Spence by hitting her with a golf club, burning her hand with an iron, cutting off her thumb and failing to get medical help accepted by the Crown.
Coats will serve a mminimum of 33 years behind bars while Wade will spend 30 years.
The 27-year-old southside financial adviser was snatched from a Glasgow street in April 2011.
The court heard that she was held in a flat in West Kilbride, Ayrshire, for two weeks where she was tortured and, subsequently, killed by Coats and Wade.
It took the jury five days to reach its verdict.
In a statement released by police, Ms Spence’s family said: “There is no verdict that will bring our daughter, Lynda, back or spare her the terrible ordeal that took her life.
“We will never begin to imagine her suffering or comprehend the cruelty of any person who would do that to another human being.
“We cannot begin to understand or forgive what they did to our daughter, Lynda. No words can begin to describe the heartache and pain we are suffering.”
The police officer in charge of the murder investigation, detective superintendent Alan Buchanan, said: @Police Scotland is pleased that the persons responsible for the abduction and horrific murder of Lynda Spence have been brought to justice.
“I hope in some small way this will bring some satisfaction to Lynda’s parents, who have had to endure the pain of hearing the graphic details of the horrific torture and terror inflicted on Lynda in her final days.
“Although satisfied with the verdict, the pain for the Spence family continues as due to the actions of the accused, Mr and Mrs Spence have been unable to lay their daughter to rest.
“At this time I would appeal to those convicted to show some common decency and tell us where Lynda is in order that we can get her back to her parents and allow them to grieve properly and move some way towards rebuilding their lives.”