A jury at Nottingham Crown Court found Susan and Christopher Edwards guilty of shooting William and Patricia Wycherly in May 1998.
Prosecutors said the debt-ridden Edwards collected almost 250,000 pounds (USD 425,000) by pretending her parents were still alive. In 2005 they sold the parents' home in the central England town of Mansfield, with the bodies buried in the backyard.
Police Detective Chief Inspector Rob Griffin said the couple, desperate for money, "decided an easy way to get their hands on it was to kill their parents, and that's what they did."
They used some of the money to buy celebrity memorabilia, including autographs of Gary Cooper and Frank Sinatra.
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They told friends and relatives that the Wycherlys were traveling or had moved away.
Police unearthed the bodies in October after being tipped off by a family member that Christopher Edwards had admitted burying the bodies.
The couple had moved to France but were arrested at a London railway station after emailing police to say they wanted to surrender.
They pleaded not guilty to murder. Susan Edwards testified that she had been provoked into shooting her mother after her mother killed her father.