Bronko Hoang is the sole survivor after his heavily pregnant wife Katherine and a 17-year-old learner driver died when Richard Moananu's car ploughed into theirs in Orchard Hills, western Sydney, in September 2018.

Moananu, now 31, pleaded guilty to two counts of manslaughter and one count of aggravated driving causing grievous bodily harm on Thursday in the Penrith District Court, and asked Judge Mark Buscombe to take a number of other matters into account.

The court earlier heard Moananu had been drinking from 10.30am to 6.45pm on the day of the crash and returned a .204 blood alcohol reading.

He was also driving on an expired licence when he veered onto the wrong side of the road, travelling more than 45km/h over the speed limit.

Mr Hoang, who awoke from a coma in hospital, said the nurses had to "tie him down" as they continually reminded him of what happened.

He recalled watching a video of his wife carried in a coffin and buried.

"Today I question who is being punished, while you sit behind bars the rest of my family and me are in the same boat," Mr Hoang told Moananu.

"The result of your actions make a horror movie seem like child's play," he said.

"You decided to be judge, jury and executioner, decided to play god....the end result... you had to take people's happiness, hope and future away."

After saying he will never have a memory of holding his newborn twins, he offered Moananu an "olive branch" to help him with his troubles.

"After this is over I want to sit down with you and get to know your story," he said.

Ms Hoang's children were due to be born the following week, the court heard.

Moananu gave evidence during his sentence hearing on Thursday saying he wished it was him who died that day.

It kills me inside....I never meant to hurt anyone that day I wish more than anything I could take it back" he said.

He spoke about a broken childhood home in New Zealand with alcoholic parents who had gambling addictions, and a father who brutally bashed his wife and children.

On the day of the collision Moananu went to a pub to play the pokies after rain prevented days of him working as a labourer.

His last memory was walking into a pub in St Mary's and drinking to "calm his nerves".

He never saw his drinking or gambling as a problem "until it was too late".

Katherine Hoang's mother Perfecta Gordon told the court losing a child felt like a life sentence.

"Before we lost her my husband and I used to wake up in the morning and say to each other what a beautiful day... we can't even share that anymore," she said.

"There is no more beautiful days in our life, now our home is quiet and empty and full of sadness, the happiness is gone."

Moananu's barrister Tony Evers said his deprived childhood meant he had no "skills" to address his problems, but before that day had been described by numerous accounts as a kind, gentle and caring man who went out of his way to help others.

Moananu is due to be sentenced on November 5.

Australian Associated Press