Ponticello also spoke about the love between Swedish-born Lars and Italian-born Vivian, saying they were inseparable and the tragic end "makes absolutely no sense".

"I always thought we would grow old together," he said.

"They are together and always will be ... You will always be remembered and in our hearts forever. Rest in Peace."

Craig Whitall, 50, was driving the other car and also died instantly. He is reported to be a serial traffic offender who was driving home from a methadone clinic when his car collided with the family of four.

The Daily Telegraph reports Whitall had more than 60 convictions and been jailed for driving while disqualified but was still behind the wheel. His family have mourned the loss of their "awesome father"

"He did the best he could and you couldn't ask anymore of him," his son Shane told Seven News.

His mother Trish said she didn't like hearing people speak badly about her son.

"He was very private and didn't like people talking about him but the worst part is, he has grandkids that can read, that are listening to it," she said.

Police would not comment on the specific case, but said people should not drive under the influence.

Methadone is commonly taken as a replacement for heroin and other opioids as part of treatment for drug dependency, with users often travelling to government-run methadone clinics across the state.

A NSW Health spokeswoman said the department had comprehensive clinical guidelines for patients participating in opioid treatment.