Mohammed Yousaf, 65, was murdered while he slept on 18 September 2016, Preston Crown Court was told.
Muhammed Arif, 45, of Washington Street, Accrington, was jailed for life to serve a minimum of 32 years.
His lover Rukhsana Bibi, 38, of Wood Street, Todmorden, received a life term with a minimum of 28 years.
The pair, who were secret lovers, had denied murder.
The court heard Arif and Bibi took out a fraudulent life insurance policy worth £244,000 on Mr Yousaf, who Bibi had married two days after divorcing Arif's brother in April 2016.
Lancashire Police said Bibi withdrew £24,000 from Mr Yousaf's savings account over four months.
Mr Yousaf, of Granville Road, Accrington, visited a solicitor with Arif and drew up a new will leaving everything to Bibi.
Police believe Mr Yousaf was murdered at his home on September 18, although his body was not discovered until three days later.
He had suffered a dozen blows to the head and a slashed throat.
Bibi was out of the country at the time of his death, but CCTV footage from a nearby pub on September 18 showed Arif's car driving to and from Granville Road three times that evening.
DNA evidence found at the scene and in Arif's car, along with mobile phones, CCTV footage and financial transactions carried out by the defendants, built up a picture of collusion between Bibi and Arif to strip Mr Yousaf of his assets, before killing him.
Det Ch Insp Joanne McHugh said this was "ruthlessly planned" by Arif and Bibi, who manipulated a vulnerable and gentle man.
"Mohammed Yousaf's death is nothing short of the cold-blooded assassination of a wholly innocent man," she said.
A pensioner suffered a dozen blows to his head and had his throat slit in a plot by two lovers who wanted his life insurance, a court heard.