S Wongaway, 32, D Wongaway, 27 and D Mumu, 35, died instantly when their car slammed into three trees in Alice Springs on December 25, 2019.
The 27-year-old driver sped through suburban streets after a police patrol car fitted with automatic number plate recognition detected that his Mitsubishi Outlander was unregistered and briefly attempted to stop him.
"The reason for them travelling so fast on a suburban road was that they feared police were attempting to stop them due to being intoxicated," Territory coroner Greg Cavanagh said in his inquest findings published on Monday.
The police did not turn on their flashing lights or siren and, after seeing the Outlander speed up and pass other vehicles on the wrong side of the road, pulled over and stopped.
Mr Wongaway's Outlander reached more than 100km/h as it fled before it collided with a ute and hit a kerb and a tree, and flipped.
"Less than 30 seconds later two siblings and a partner travelling in the vehicle were dead," Mr Cavanagh said.
"It was an immense tragedy and left their families and community absolutely devastated."
Passengers Ms Wongaway and Mr Mumu died after they were thrown from the car as it flew 13m through the air and hit two more trees further down the verge.
A forensic pathologist found Mr Wongaway had a blood alcohol level of .24 per cent. His body was found in the driver's seat with a seatbelt on. The Outlander was cut in half and barely recognisable.
After the accident, their families asked if police had chased the trio and whether their deaths should be classified as deaths in custody.
They also said Mr Wongaway's unregistered car was not a serious offence and did not warrant a traffic stop because the police could have used the vehicle licensing system to find his name and address.
Mr Cavanagh found police had not pursued Mr Wongaway's Outlander and even if they had it was unlikely the deaths would be deemed as deaths in custody.
He said the police were not in control of the trio when they died and they were not in custody.
"When the police undertook the U-turn they had the intention of stopping the vehicle. They sped up to try and close the distance to the vehicle," he said.
"If they had closed the distance they would have signalled for the Outlander to pull over, most probably with lights and sirens. However, the Outlander sped away."
Mr Cavanagh said the officers involved were performing their duty as expected of them by the police force and the community.
He also found the police would not have been able to locate Mr Wongaway using the licensing system because he had not transferred the Outlander into his name after he bought it from a local car yard a month earlier.
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