Xavier Abreu, 10, and his younger brother Peter, nine, were killed when a Subaru Impreza sedan they were inside crashed into a tree at Monterey on August 25.

The driver, a 33-year-old man, was charged over the incident and remains before the courts.

Following extensive investigations, police have charged a second man after new information was revealed about the moments that lead up to the crash.

Police will allege the Subaru Impreza was involved in a street race with a silver Audi A4 before the Subaru driver lost control of the vehicle, crossing to the incorrect side of the road and crashing into the tree.

A 24-year-old man has been charged with two counts of aggravated dangerous driving occasioning death, organising and promoting a road race and two counts of failing to stop and render assistance after impact causing death.

Investigators attended a Roselands home about 10.30am on Wednesday and seized an Audi A4 for forensic examination.

About 3.30pm, the 24-year-old man attended Campsie Police Station and was arrested.

He was refused bail to appear before Bankstown Local Court on Thursday.

His licence was also suspended.

A 24-year-old woman, who was allegedly in the passenger seat of the Audi at the time of the crash, was also arrested and charged.

She was taken to Kogarah Police Station and charged with concealing a serious indictable offence.

The woman was granted strict conditional bail to appear at Sutherland Local Court on October 17.