Shane Coughlin, 21, of Garden Grove, told Eyewitness News it's a trip that he'll never forget.
"Just given the fact that it was the last time the five of us were physically together... I wouldn't want to change it for the world," he said.
According to the California Highway Patrol, the family of five was driving on the freeway just south of Crenshaw Boulevard when a speeding driver hit them from behind, causing their car to flip last week.
Shane, his sister and their mother survived.
Shane said his 24-year-old brother, Luke, was his twin flame.
"He just knew how to make everyone laugh and how to make everyone smile."
He pointed to a photo of Luke in a graduation cap and gown posing with a Starbucks cup for his senior portrait.
"My mom wanted us to take a picture with something that got us through high school," he said.
When asked about his 57-year-old father, Gregory Coughlin, Shane described him as his hero. He added the U.S. Postal Service mailman was generous, humble and always looking to inspire his three children.
"My dad was my life teacher and I want to be a teacher for everyone else."
A GoFundMe account has been set up to support the family.
"Just knowing that there are so many people out there that care for me and care for my family, most importantly, it speaks volumes to me," Shane said.