Dipjoy Saha(30) and his younger brother Bitanjoy (27) were arrested last night by CID, who had taken over the investigation into the alleged matricide.
Based on their confession, the two hired killers Krishna De and Ranabir Lodh were also arrested last night, the police said.
Santa Saha, whose husband is an employee of the engineering cell of Tripura police, was killed at their government quarters at Shyamali Bazar, a high security area of the capital town, on August 17.
She was known to have often objected and tried to stop her sons from being involved in criminal activities.
The two sons were produced at the Additional Chief Judicial Magistrate Rajib Bhattacharya's court today and was remanded to police custody for five days.