Preliminary inquiries showed unidentified assailants killed the family members with iron rod or similar blunt objects, DSP, Panposh, Tushar Kant Jena said.
The deceased were identified as Milko Badaik (30), his wife Arati (25) and their son Adikunj (3), he said adding that the family hailed from Jharkhand and Milko was working as a mason.
Investigation was in progress and police seized certain articles from the spot. "It seems more than one person were involved in the crime," the DSP said.
Bandhua Majhi, 45 and Chuku Majhi, 42 were attacked with a hammer by some persons who left them critically injured, Jena said.
They were later shifted to Rourkela Government Hospital, he said.