The court of Additional District Judge Anil Kumar Vashistha awarded the jail term to Tiryugi Narain and Badri Vishal yesterday after it found the two guilty of killing their sister.
A fine of Rs 35,000 each was also imposed on them.
In May 1987, Tiryugi and Badri had immolated their sister in Visheshwarganj area after they found her in a compromising position with a youth, the prosecution counsel said.
Initially, the brothers had informed the police that the girl had committed suicide, but postmortem revealed it to be a case of murder.