Alina Kauffman, 24, and her 15-year-old brother Ernesto Salazar were killed when a black Mercedes hit their car just 200 metres from their Heckenberg home in Sydney's southwest on Friday night.
Witnesses told police three young men inside the Mercedes ran from the scene before driving off in a Volkswagen Golf.
The alleged Mercedes driver Johnson Kokozian, 20, appeared in Parramatta Local Court via videolink on Sunday, charged with multiple offences including two counts of dangerous driving occasioning death.
He was refused bail and is due to appear at Liverpool Local Court on Wednesday.
NSW Police Deputy Commissioner Paul Pisanos said officers were keen to speak to a number of other people who witnessed the crash or were passengers in other vehicles.
Mr Pisanos said police had noticed an increase in drivers not complying with speed limits following COVID-19 lockdowns.
"Road rules are centred around safety for the individual driver and safety for members of the community," he said on Monday.
"It seems to us there is a blatant disregard for the road rules.
"It's unacceptable because as you can see through ... the Heckenberg incident and others, they lead to absolutely catastrophic consequences."
More than $20,000 has been raised via a GoFundMe page for Alina and Ernesto's mother Angelina and sister Ayeanna.
The page was set up on behalf of Ms Kauffman, a single mum, to help with the funeral costs for her two children.
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