The heads of three of them were smashed with a stone while the fourth had bullet wounds from a revolver, police said.
The victims have been identified as Nitin Joshi, Balram Chaupanne, Pritam Gharat and Ramdas Patil, all hailing from Panvel, police said.
The farmhouse was owned by Datta Patil, a local agriculture group activist, whose nephew - Ramdas Patil - was among those four killed, police said.
