The Canadian singer was 22 when her mother Sharon and stepfather Jerry - who had adopted Twain when she was four - died in a head-on collision with a truck in 1987.
At the time, Twain was living in Toronto and studying computer programming.
"I collapsed hearing that news over the phone," she told Lauren Laverne on Desert Island Discs.
"My sister called me and I could hear my little brother howling in the background."
Twain then took on the role of caring for her three younger siblings.
"The kids could not be separated after that accident – they had to stay together," she added.
Soon after, Twain became responsible for the family and her parents' business affairs.
"I leave Toronto of course and am back in the last family home we had that the kids were still living in and moved back in," she said.
"My older sister was gone and was married with two children and had her own life in another town. I had to do a lot of things I knew nothing about like take out a second mortgage for the house to sustain what is going to happen next."
Twain said she then had to organise selling equipment from her parents' business and was in lawyers' offices frequently, navigating insurance affairs as passengers in the vehicle and the truck driver were suing.
"There were so many complexities to the accident itself. I wasn't allowed to grieve because I was thrown into this state of guardianship and executor, plus I don't have a job," she continued.
After finding a job at a golf resort in a town six hours from their hometown, Twain later moved there with her siblings as it offered them a steady income and allowed her sing.
Twain also shared details of her parents' abusive marriage - saying she felt she had to "protect" her mother.
"It was bad. He would choke her a lot and do things that don't end well," she said.
Twain would eventually meet and marry record producer Robert John "Mutt" Lange.
They were married in 1993 and had son Eja in 2001, however separated seven years later after he had an affair with her best friend, Marie-Anne Thiebaud.
It was her friend's husband, Frederic Thiebaud, who alerted her to the affair.
"I didn't know anything that was going on, but he then took the blinders off and told me. I didn't believe him and told him he was imagining things," she said.
Twain then recalled how they both decided to "let their (marriages go)".
"And in that time we found each other. I found out what a beautiful person he was," she said
She then said that she would "treat him better".
Twain and Thiebaud then married in 2011.
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