An elderly couple and their son were killed and four others critically injured during a fight over an alleged land dispute between two families in Tripura's Dhalai district, police said on Friday. A police official said the kin of the two families attacked each other at Kamalpur on Thursday afternoon, injuring seven people. Of the seven injured persons, Rajani Das, 70, died on his way to Agartala Government Medical College and Hospital, while his wife Bilasi, 67, and son Pratyus Das, 41, succumbed to their injuries early on Friday. The injured persons, including a woman, are currently undergoing treatment at the Dhalai district hospital. The police have detained two people in connection with the incident.