Additional District and Sessions Judge Prakasan also imposed a fine of Rs 5,000 on Balamurugan, Ramakrishnan, Vilvalingam and Muniasamy.
The court acquitted Balamurugan's mother and another relative. A minor accused has been referred to Juvenile home.
According to the prosecution, Balamurugan had approached the deceased Dharmalingam, to wed his daughter to him. As he refused, there was a heated exchange and Balamurugan and his relatives hacked him to death.
Police had registered cases against eight persons. One of the accused had died during the trial.