Awarding the punishment, the court of District and Sessions Judge here termed the case as "rarest of the rare".
The court also sentenced the couple's accomplice Jaiveer to life imprisonment.
The conviction took place on March 4 and the quantum of punishment was announced today.
According to the prosecution, Sonam Dagar was in love with Naveen Dagar of the same village and clan.
Apprehensive that her family will reject the relationship, Sonam served food laced with poison to her parents, brother, grandmother and three cousins in September, 2009, it said.
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To mislead the investigators, the girl was found lying unconscious in a bathroom by the police. But the case was later cracked and the accused were arrested.
A case was registered against them under various sections of the Indian Penal Code (IPC).
Jaiveer had arranged the sleeping pills and poison.
The fourth accused in the case, chemist Omvir, from whose shop the pills were procured, was acquitted by the court.