Pirojpur District and Session Judge Md Majibur Rahman handed down the punishment.
The lifers were identified as Ezaz Sharif, 27, Akkas Sharif, 52, Shafayet Sharif, 52, Shefali Begum, 45, Happy Begum, 28 and Lima Begum, 20 in Sadar upazila of Pirojpur district.
The court also fined them Tk 10,000, in default, to suffer six months more in rigorous imprisonment.
The court also sentenced Emran, 28 of the upazila to two years in jail in the case. It also fined him Tk 2,000, in default, to suffer three months more in rigorous imprisonment.
According to the prosecution, Abul Kalam Sharif, 55 of Jhanjhania area in Sadar upazila of Pirojpur district was stabbed to death by the convicts on July 10, 2014 over previous enmity.
Hakim Sharif, brother of the victim, filed a case with Sadar Police Station on the following day.
On May 4, 2015, police submitted a chargesheet against eight people.
After examining records and witnesses, the court acquitted one person as allegations brought against him could not be proved, reports UNB.