District Judge Ramathilagam also sentenced them to an additional five years RI 'for evading the truth' and slapped a fine of Rs 10,000 on them.
The sentences would run concurrently, the judge said.
The 21-year-old man was found dead in a forest area in Kolli hills in the district in February 2011.
The prosecution case was that Devachandran (41) suspected his wife Ponkodi of having an affair with Balakumar. He berated her for it and they decided to do away with him.
The case came up yesterday and the magistrate convicted them.