Salim Hamze, 18, and Toufik Hamze, 64, were shot while sitting in a car in Guildford last October.
Salim died at the scene, while Toufik was taken to hospital, where he died.
Earlier this year, detectives charged a 25-year-old man over his alleged role in the incident.
Now, a 20-year-old man has also been charged with two counts of murder.
Police have alleged he had direct involvement in planning and coordinating the cars used in the shooting.
The 20-year-old was arrested at a Grafton jail at about 1pm yesterday.
He will face court today.
