The victims were identified as Sohel, 40, the driver of the car; Shamima, 40; Ety Begum, 35; and Ayan, 7, all from Narayanganj district.
The accident occurred around 7:30 am when a Sylhet-bound truck crashed into the car, which was carrying seven people. Two died instantly, and five others were injured, said Monayem Mia, officer-in-charge of Osmaninagar Police Station.
Two of the injured later succumbed to their injuries while being transported to Osmani Medical College and Hospital.
The family had been traveling to the Sylhet Hazrat Shahjalal (RA) shrine from Rupganj upazila in Narayanganj. Police believe the accident may have been caused by poor visibility due to dense fog.
Authorities recovered the bodies and sent them to the local hospital morgue for further procedures.