Police say Naqeebullah, a refugee from Afghanistan, had married without the consent of the family four years ago.
Mujahid, the girl's brother, went to meet the couple at the latter's residence.
As the clock struck midnight, he, along with his brothers Qudratullah, Fazal Nabi, Abdul Nabi and Gul Rehman opened fire on their sister and her husband.
The couple succumbed to their injuries on the spot.
Naqeebullah's family have registered a complaint with local police, and investigation into the case has begun.
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