Surviving Colorado sons mourn parents, young sisters after deadly crash; "I was really just hoping it was a nightmare."

A Thornton family is experiencing deep loss, as two brothers mourn four beloved family members, who were killed in a fiery crash over the weekend. 

Family members told CBS Colorado on Monday Francisco Díaz, 49, Beatriz Núñez, 49, Paola Díaz, 15, and Nataly Díaz, 10 all died when they were hit in their vehicle by another driver on Saturday. They leave behind surviving family members Adam and Daniel Díaz, 20 and 22.

"We're really close to our family; we all live together," Daniel told CBS Colorado.

Adam and Daniel are the big brothers in a close-knit family of six. On Saturday evening, their parents, Francisco and Beatriz, took their sisters on a grocery run to Walmart in Thornton. Within minutes of leaving their Thornton family home, the worst case scenario happened.

"I was going to eat, and as soon as I was gonna walk in, I get a notification saying that my little sister Paola has been in a crash -- detected SOS," Daniel said. "That's when I ran out of the restaurant. I get in my car; I call my brother, tell him if they're OK."

"None of them were really answering the phone, so that's when I headed over," Adam told CBS Colorado.

Adam rushed to the scene, but his loved ones were already beyond the ability to be rescued by first responders.

"I got there pretty quick, but everything was already in flames. There was nothing they could do," Adam Díaz said.

All four family members inside the truck lost their lives.

"It just didn't feel real. I was really just hoping it was a nightmare," Adam explained.

Now, Adam and Daniel are left to pick up the pieces.

"Getting out of work and seeing an empty house with nobody there, all this stuff that they wanted to do that we'll never be able to do with them anymore," Adam said.

They're reckoning with the loss of their hardworking father, a fabricator who also "knew a little bit about everything," his sons shared.

"He's the one that taught me everything, which just hurts because now I feel like I don't really know anything," Adam said. He says his father was helping him paint his car and make plans to start a business.

They're also missing a caring mother, who worked as a cleaner, and would always wait up for her children to arrive home.

"Knowing this time that I'm gonna go out and get home, she's not gonna be waiting for me," Daniel said.

"That there's not going to be a single call asking us where we're at, what we're doing," Adam said.

Adam and Daniel's two sisters will now forever be 10 and 15 years old.

"There was Paola, who was very shy, but she was always nice to people. She was always trying to have fun, watch movies, go out to eat, draw, and all this stuff she wanted to do with us," Adam said.

Paola was in school studying health care. Her brother, Daniel, says he would often help her study.

"I took the classes too, but that was just because I was trying to outsmart her, teach her," Daniel said, as both boys shared a tearful smile.

"Nataly was more of an outgoing, always trying to dance, sing, talking to everybody, making friends everywhere," Adam said.

Adam and Daniel men say they're looking for guidance and asking for prayers. A family member is collecting funds to support them during this time.

Thornton Police Department could not share additional details about the crash but said the investigation was ongoing. The Díaz brothers say they were told by police that their family was stopped at a red light when another car that was speeding hit them from behind, causing their truck to catch fire and be pushed into the intersection, where they were T-boned by another car. The driver of the car that initially hit the family was taken to the hospital with serious injuries; their current condition is unknown.

The two young men are now leaning on extended family as they plan a funeral for four. The home they all shared now feels empty. The brothers' goal was to one day buy their parents their own home. It's a dream that has now changed, but they still haven't given up on it.

"We're probably gonna try to eventually move out to a home that we can call just ours that we can own," Adam said. "My dad and my mom wouldn't just want us to give up; we gotta keep going. It's what they would want, and not to give up no matter what,"

Two brothers are now finding a way to move forward with the only thing they have left -- each other.

"I'm really grateful I still have him," Daniel said.

"Yeah, I could not have done this by myself," Adam agreed tearfully as the two brothers clutched each other's hands.