A .315 bore rifle with seven cartridges and one 12 bore DBBL gun with 10 live cartridges were seized from the duo's possession.
Ponty and Hardeep, who had an ongoing property dispute, were killed in a shootout at their Chattarpur farmhouse on November 17.
Police had earlier arrested Namdhari and his personal security officer Sachin Tyagi in the case. Namdhari has been booked on charges of murder in the case.
Namdhari had brought a number of associates, who had assisted Ponty Chadha in smooth sailing of his various businesses in UP, Uttarakhand and Punjab, with weapons, hockey sticks and baseball bats to facilitate forcible possession of a farmhouse in Chattarpur.
In this regard two criminal cases, one of forcible dispossession in which Hardeep Singh was murdered and other of murder of Ponty Chadha were registered.
Prior to the twin arrests, eight persons -- including Namdhari and his gunman Tyagi -- were arrested in the case, DCP (crime and railways) SBS Tyagi said.