Eatery owner Shyam Singh Verma, 57, and his son and manager Mayank Singh, 28, were shot dead by four armed men who had come to dine at the eatery in Nangli Dairy area of Najafgarh on Wednesday night.
The accused, who were drunk, asked a waiter to point the cooler at the eatery in their direction.
Mayank objected to this, at which one of the accused then forcefully pointed the cooler towards their table. Mayank tried to stop him, resulting in a scuffle between the two.
"He abused and dragged Mayank," a police officer said, adding that the other accused joined in and started beating the owner's son.
Shyam Singh, who was sitting at the cash box, tried to rescue his son. At this point, one of the men took out a pistol and fired at Mayank.
Shyam died on the spot while his son succumbed to his injuries at a private hospital in Dwarka, the officer said.
The accused fled and are absconding. There were at least 15-20 people at the restaurant and some of them informed the police.
The police said they have identified the suspects, who have a criminal background. Police is searching for the accused.