Another 10 police officers also charged in the case have already died.
The policemen were found guilty of staging a pre-arranged extrajudicial killing known as a fake encounter.
Encounters are partly a response to India's slow and dysfunctional criminal justice system, correspondents say.
Police often see cases evaporate as trials are delayed and witnesses turn hostile.
The latest high-profile case to come to court dates back 25 years ago to when a group of Sikh families, including children, was travelling by bus through the state Uttar Pradesh in northern India after visiting holy sites.
Police officers stopped the bus in Pilibhit and forced some of the men to get out.
Later, joined by more policemen, they divided the Sikh men into groups, led them into the jungle and shot them dead.
Why India's 'fake encounters' are shockingly common
Afterwards, police lied about what happened. They claimed that the men were militants and armed - at the time, there had been a spate of attacks in the region by Sikh groups fighting for a separate homeland.
The Central Bureau for Investigation (CBI) said that the motive for the killings was to earn awards and recognition for killing "terrorists", NDTV reported.
The court in sentencing the men said that police officers who were holding important posts must be behind the killings , but the CBI had kept them away from the investigation, The Indian Express reported,
The court said that the CBI officer investigating the case was not fully free to take decisions relating to it without constantly referring to his senior officers and that several people who should have been accused were instead set free or not charged.
Relatives of those killed protested outside the courtroom against the sentences, which they argued were too lenient.
"We are not satisfied with the judgment. The accused should be given death sentences. We will file an appeal," Balvinder Jeet Kaur, whose husband Baljeet Singh died in the encounter, told the Indian Express.
Forty-seven police officers have been sentenced to life in prison by a special court in India for killing 10 Sikh pilgrims in 1991 and then lying in an attempt to justify the shootings.