Underneath a white tarpaulin roof, behind razor wire and barking police dogs, Wendy Ramírez Penosa and her two teenage sons stood before an immigration judge sitting 30 miles (48km) away from them. Through tears, they begged the court to keep them safe.

“My children have been threatened with kidnap,” Ramírez said through a translator on Monday afternoon, describing threats both in Mexico and in Honduras, her home country. “They said I would be forced to work in a brothel.”

“I don’t want to be taken back to Mexico. They killed my father [in Honduras]. That is why we are fleeing.”

Ramírez was pleading her case at one of Donald Trump’s newly built tent immigration courts, erected a few feet from the US-Mexico border in Brownsville, Texas. These makeshift courts, constructed last September, have been inaccessible to the public, but play a central role in the president’s “Remain in Mexico” (Migrant Protection Protocols) policy, which advocates describe as an attempt to curtail the right to asylum in the US by sending migrants back to Mexico as their cases are processed.

The immigration court tents in Laredo, Texas. Photograph: Veronica Cardenas/Reuters

Of the 56,000 cases brought under MPP only 117, or 0.2% of cases, have so far led to asylum relief for applicants, according to data from a monitoring project at Syracuse University. On Tuesday, House Democrats launched an investigation into the process, describing it as “a dangerously flawed policy that threatens the health and safety of legitimate asylum seekers – including women, children, and families” that “should be abandoned”.

The Executive Office for Immigration Review (EOIR), which is the arm of the justice department overseeing immigration court, declined to answer certain questions for this report, citing “pending litigation”. They referred other questions to the Department of Homeland Security (DHS) who did not respond despite multiple requests.

The Guardian is one of the first media organizations to observe proceedings in Brownsville after the tent courts here, and others in Laredo, were opened to the public at the end of last week.

The court in Brownsville, a sprawling complex of white tents, is built on a parking lot next to a US Customs port of entry that is attached to a bridge over the Rio Grande, which links the US to Mexico. Asylum seekers are bussed in by DHS officials, and line up, single file along floors covered in artificial grass, many holding babies and toddlers, and are then ushered into a courtroom under guard. They are sent back to Mexico after the proceedings, often carrying belongings in clear plastic bags.

Judge Barbara Cigarroa appeared via video link on a large TV screen inside a portable building that was listed as Courtroom C. The judge, softly focused on the monitor, sat at an immigration court in the city of Port Isabel. The voice of a government lawyer was audible on the link up, but their face could not be seen by the roughly 23 asylum seekers present for the afternoon session.

“I’m sorry to hear that,” said Cigarroa to Ramírez as she articulated her fears. The judge encouraged her to find an attorney to assist with her asylum application.

But, like the vast majority of those seeking asylum in the US, Ramírez could not afford one – of the 5,596 cases completed at this court in Brownsville, just 81 people had a lawyer, according to public records.

“I prefer that you send me back to Honduras and my children to the US,” she said. “Even if they kill me, I don’t care. As long as my boys are OK.”

Of the 56,000 cases brought under Migrant Protection Protocol, only 117 have resulted in asylum relief for applicants. Photograph: Eric Gay/Associated Press

The judge set her next hearing date for 10 March, and instructed DHS to interview her and her children after they articulated their fears of returning to Mexico.

Advocates suggest anecdotally that around a third of asylum seekers in these courts express fears of returning to Mexico, where extortion and threats from cartels in border areas is common. But for those without attorneys, it is unheard of to be taken out of the Remain in Mexico program and held in the US despite articulation of fears, said Andrew Udelsman, a legal fellow at the Texas Civil Rights Project who is monitoring the Brownsville tent court.

“The purpose of this policy [MPP] is absolutely to deter people from seeking asylum, making it as inconvenient, difficult and dangerous as possible,” Udelsman said. “This is the next development on from the child separation policy – designed to deter people from coming to this country.”

The justice department and DHS would not comment on Ramírez’s case and did not provide the numbers of asylum seekers in the Remain in Mexico program articulating fears of return. The Guardian has been unable to verify if Ramírez, and at least six other asylum seekers who articulated fears of returning to Mexico – two others citing kidnap or forced prostitution threats – were returned to Mexico after their hearings on Monday.

Although the tent courts are now technically open to the public, their operations remain shrouded in opacity.

The Guardian was not allowed to move between courtrooms during a visit on Monday, and was escorted into a single public gallery by private security guards. The Guardian was earlier held in a separate waiting area, under guard, away from other members of the public. Udelsman was blocked from entering the facility on Monday because he brought a pen and paper, which an armed Department of Homeland Security police officer outside the facility said was a security risk.

The Guardian was allowed to enter with stationary, but was prevented from viewing the court’s docket list, meaning the spelling of names and the number of cases before the courts could not be verified. Only initial hearings, known as Master Calendars, were open to the public, leaving merits hearings – where an asylum case is finally decided – inaccessible.

Across the Rio Grande, in the Mexican town of Matamoros, an encampment of about 2,500 asylum seekers has been erected since the start of the policy.

Dr Dairon Rojas, a 28 year-old Cuban seeking asylum, works in a makeshift medical clinic in an encampment in Matamoros, Mexico. Photograph: Oliver Laughland/The Guardian

The hundreds of tents are home to mostly central Americans waiting for their days in court. Aid has been slow to arrive here, and there remains no official Mexican or US government presence. Instead, volunteers and NGOs have established makeshift schools, legal centers, sanitation services and a medical clinic offering support to migrants. Many of these facilities are being staffed by asylum seekers themselves.

Dr Dairon Rojas, a 28-year-old Cuban seeking asylum, works as a general practitioner as he awaits his next court hearing on 27 February. He said there remain ongoing health concerns related to the spread of bacterial infections due to the closed quarter living conditions.

“Sometimes we don’t have everything a patient needs. Blood tests. X-rays. We can’t do that here,” he said, adding that complicated cases are referred to Mexican health authorities.

But, at the back of his mind, Rojas continued to worry about his own case as well.

“You can’t imagine the stress,” he said. “All I want is to live and work in the US.”