A devastated mother posted on her Facebook page that her three daughters, their father and his wife were among those presumed dead after flames engulfed a dive boat off southern California over the holiday weekend.

“It is with a broken heart ... 3 of our daughters were on this boat. As of now they are still missing,” Susana Rosas of Stockton, California, wrote on Tuesday morning. “The authorities do not have much to say to us.”

Rosas posted that her daughters – Evan, Nicole and Angela Rose Quitasol – were with their father, Michael Quitasol, and stepmother, Fernisa Sison, and thanked people for their prayers and support.

The family of five was among 34 people presumed dead in the blaze. All were sleeping below deck when the fire started early Monday. Other victims included students from a northern California charter school, and a marine biologist who owned the diving company that was leading the tour.

Five crew members were rescued, and the bodies of 20 victims have been recovered so far. Many need to be identified by DNA analysis, and officials are collecting samples from family members.

Evan Quitasol was a nurse at St Joseph’s Medical Center of Stockton, where her father and Sison had worked after attending nursing school at San Joaquin Delta College.

Rosas’ husband, Chris, told the Los Angeles Times that Nicole Quitasol worked as a bartender in Coronado near San Diego and her sister, Angela Rose, was a science teacher at a middle school in Stockton, a city in northern California.

The sisters were on the trip to celebrate their dad’s birthday, Chris Rosas said. He described them as “the most kind, most loving people I’ve ever met – and I’m not just saying that because they’re family”.

Sison also worked at the college teaching first-year nursing students full-time in 2005 and 2006 and later as an adjunct instructor, said Alex Breitler, the school’s spokesman.

“Everybody’s devastated. It’s a totally unexpected thing that happened,” said Dominic Selga, Sison’s ex-husband. “What caused the fire? That’s the big question; that’s what we all want to know.”

Selga said his ex-wife’s family had been on the boat “five or six” times and had been diving for a decade. Selga said the two families spent Mother’s Day and Father’s Day holidays together and called the Quitasols “great people”.

Also below deck were students from Pacific Collegiate school in Santa Cruz. School director Maria C Reitano declined Tuesday to say how many students went on the trip, which was not sponsored by the school.

Scott Chan, a physics teacher at American high school in Fremont, was also on board with his daughter, said Brian Killgore, a spokesman for the Fremont Unified School District. The district said in a statement that Chan taught advanced placement physics classes for the past three years at the school and was well liked.

Scott Chan, a physics teacher at American High School in Fremont, was aboard the ill-fated dive boat, a district representative has confirmed. Photograph: AP

“His students knew him to be an innovative and inspiring teacher who developed a passion for physics among his students,” the district said in a statement. “His loss is a tremendous tragedy for our school district.”

ABC affiliate KNXV-TV in Phoenix reported that an Arizona couple, Patricia Beitzinger and Neal Baltz, were also on the trip.

“They went to heaven doing something they loved together,” Neal’s father, John Baltz, told the station.

Brett Harmeling of Houston said that his sister Kristy Finstad, 41, was leading the scuba tour off Santa Cruz Island, part of California’s Channel Islands.

Harmeling thanked everyone in a post on his Facebook page for their “unconditional love and support during this incredibly tragic time”.

Finstad was co-owner of Worldwide Diving Adventures, a company founded by her mother in the 1970s and based in Santa Cruz, about 250 miles (400km) north of Santa Cruz Island.

Finstad knew the area well, having done hundreds of dives in the Channel Islands, where she first swam as a toddler with her father. Harmeling described his sister to the Los Angeles Times as extremely strong-willed and adventurous.

“If there was a one percent chance of her making it, she would have made it,” Harmeling, 31, said.

Finstad studied damselfish and corals in the Tahitian Islands, dove for black pearls in the French Polynesian Tuamotus Islands and counted salmonids for the city of Santa Cruz, where she lived. She also did research for the Australian Institute of Marine Science and wrote a restoration guidebook for the California Coastal Commission.

“My mission is to inspire appreciation for our underwater world,” she wrote on her company’s website.

She and her husband had just returned from sailing across the South Pacific. It was part of their 10-year plan that started on the back of a napkin in 2006.

They left from the Channel Islands in 2015 on the journey and planned to return in 2018. Before they set off, Finstad wrote: “Our new boss is King Neptune: when it blows we hunker down; when there’s surf we paddle in; when there’s rain we wash up. In terms of timelines, the best we can do is point in the right direction.”