Samad Dawood, the brother of Shahzada Dawood, one of the passengers who died in the submersible, said losing his brother and nephew, Suleman Dawood, is heartbreaking.

"This is beyond what you could ever imagine in terms of the kind of hardships and struggle that we've had. I think what we've seen is enormous tragedy and devastation and a lot of emotions. Obviously we were hoping to hear some good news about the rescue and them coming back. It was heartbreaking to find out that that's not the case," Samad Dawood told ABC News.

Samad Dawood said his brother had a strong sense of adventure and curiosity about the world.

"He was always the kind of person who has this incredible love for the world," Samad Dawood said.

"He inspired us curiosity. And he was a guy who just wanted to go out there, experience what the world had to offer, even though he he himself pushed himself to do it. So they made adventures to go to Antarctica, to go to Greenland and to go to Africa and go to the rapids," Samad Dawood said.

This sense of adventure was passed on to Shahzada Dawood's son, 19-year-old Suleman Dawood, who was also in the submersible. Suleman Dawood had traveled to all seven continents, according to Samad Dawood.

"He was so filled with humbleness and gratitude," Samad Dawood said.

"We're deeply grateful for all the support and the love and the effort that the people have made, working tireless nights being optimistic in giving a sense of hope, giving that transparency to us. But obviously we were devastated as a family ... that we couldn't get them back safe," Samad Dawood said.

-ABC News' Octavio Cadenas, Dr. Jennifer Ashton and Victor Ordonez

Renowned Hollywood director and Titanic researcher James Cameron said he believes the carbon-fiber composite construction of the submersible's hull was the "critical failure" that led to its implosion during a deep-sea tour of the Titanic wreckage.

"You don't use composites for vessels that are seeing external pressure. They're great for internal pressure vessels like scuba tanks, for example, but they're terrible for external pressure," Cameron, who famously directed the Oscar-winning film "Titanic," told ABC News' George Stephanopoulos in an interview Friday on "Good Morning America."

"This was trying to apply aviation thinking to a deep-submergence engineering problem. We all said that it was, you know, a flawed idea and they didn't go through certification," he continued. "I think that was a critical failure.

"The thing that's insidious here," Cameron added, is the way these materials "fail at pressure."

"They fail over time, each dive adds more and more microscopic damage," he said. "So, yes, they operated the sub safely at Titanic last year and the year before, but it was only a matter of time before it caught up with them."

OceanGate CEO Stockton Rush, who was among the five crew members killed on the submersible, had previously defended the decision to manufacture the Titan with the material, saying he believed a sub made with carbon fiber would have a better strength-to-buoyancy ratio than titanium.

Bob Ballard, the oceanographer and explorer who discovered the Titanic wreckage in 1985, told ABC News that he expects the investigation into what happened "will go on for quite some time."

"There will be now a very systematic survey. I've done this before," he said during the interview Friday morning. "The [remotely operated vehicles] are going to do a very, very precise, systematic mapping that will collect the photography and high-definition imagery and they'll also be recovering the objects."

The Hussain and Kulsum Dawood family has issued a statement expressing their condolences.

"It is with profound grief that we announced the passing of Shahzada and Suleman Dawood," the family said. "Our beloved sons were aboard OceanGate's Titan submersible that perished underwater. Please continue to keep the departed souls and our family in your prayers during this difficult period of mourning."

"We are truly grateful to all those involved in the rescue operations," they continued. "Their untiring efforts were a source of strength for us during this time. We are also indebted to our friends, family, colleagues and well-wishers from all over the world who have stood by us during our hour of need. The immense love and support we receive continues to help us endure this unimaginable loss."

"We extend our heartfelt condolences to the families of the other passengers on the Titan submersible," the family added. "At this time, we are unable to receive calls and request that support, condolences and prayers be messaged instead. Details of their final rites in this world will be announced soon."

-ABC News' Habibullah Khan

Engro, the company sub passenger Shahzada Dawood worked as the vice chairman, offered its condolences for both Dawood and his son, Suleman Dawood, on Thursday.

"With heavy hearts and great sadness, we grieve the loss of our vice chairman, Shahzada Dawood, and his beloved son, Suleman Dawood," the company said in the message. "Our thoughts and prayers are with the Dawood family at this tragic time."

"We extend our heartfelt condolences to the family, colleagues, friends and all those around the world who grieve this unthinkable loss," it added.

-ABC News' Habibullah Khan