The accused, Krishan Singh, also stabbed himself, but was rushed by neighbours to a government hospital in Faridkot, they said.
Reena (24), Mangal Singh (60) and Mohinder Kaur (55), residents of Zira, died in the last night incident, the police said.
Krishan, a resident Moga district's Dune Ke village, entered Reena's house by climbing its wall and and allegedly attacked them, they said
When his brother-in-law Saab Singh and sister-in-law Amandeep tried to stop him, he attacked them too, due to which they got critically injured, the police said.
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Senior police officials, including SSP Ferozepur Gaurav Garg, reached the spot.
The SSP said that the accused has been referred to the Government Medical College in Faridkot while Saab and his wife have been admitted to a local hospital.
Krishan's wife had left him due to some differences and had started living with her parents here.