Additional District and Sessions Judge Suresh Chand Saini also imposed a total fine of Rs eight lakhs on them, prosecution said.
60 per cent of the total amount will go to the families of the deceased, he said.
On July 14, 1990, Rajeshwar Singh, Omendra Singh, Dhanpal and Nathu Singh of Rapda village in Jaitipur area of Shahjahanpur were killed by armed men and their bodies were thrown in the Bahgul river.
23 people were booked for the murders and out of which six died during the course of the trial. One of them was acquitted due to absence of evidence.