The incident took place after an argument between the father and son over a tractor.
Manjeet Singh, allegedly in an inebriated condition, poured petrol on his son Sewa Singh (40), daughter-in-law Baljit Kaur (35) and the grand daughter, and set them on fire last night, Sujanpur SHO Harishan Singh said.
He then took his life by jumping into a canal.
Police said Baljeet's condition is critical.
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