The duo were arrested in the Vasant Vihar area of south Delhi. Police said one pistol and two live cartridges were recovered from them.
"Anita was Kumar's sister-in-law and had been married to his late elder brother Sri Bhagwan. Anita had developed intimate relations with Chautala," said Deputy Commissioner of Police (south Delhi) H.G.S. Dhaliwal.
"Shri Bhagwan expired around two years ago. Kumar suspected that Anita and Chautala had poisoned his brother. Anita was residing with Chautala at the time of the murders.
"Pradeep also held a grudge against Chautala as the latter had once fired at his younger brother who survived."
Dhaliwal said: "The accused along with their other associates fired multiple shots to ensure that both Anita and Chautala were dead."