The family of a couple and their three sons who were involved in a horror crash in Victoria's north at the weekend say they are "totally devastated" by the accident, and are rallying around the pair's surviving children to help them cope with the tragedy.

Her husband, 44-year-old Paul Kilmister, remains in a coma, and as such has not been told his wife and son are dead.

Eight-month-old Austin is in a serious condition with spinal injuries, while two-year-old Morgan is said to be recovering well.

Mr Kilmister's mother, Christine, said the couple's eldest son, 14-year-old Felix, who wasn't in the car, has taken it upon himself to support his brothers until his father wakes up.

"Young Felix has been talking to his Dad, even though he's unconscious, talking to him about Austin, Morgan — but he hasn't mentioned Harrison or Mummy," she said.

"So if it's true what they say and he knows what's going on, he'll know that something's wrong."

She said her family would do everything they could to support her son when he woke up and received the news.