The wife of a Kenyan man who is due to be deported from Perth on Monday is lobbying the federal government for him to be able to stay in Australia.

John Mbuthia Mwangi, 31, was handcuffed and taken into immigration detention on 14 February after being called in for an appointment with his Department of Home Affairs case manager in Perth.

He has spent the past five weeks in Yongah Hill detention centre and was told on Saturday that he would be placed on a flight to Kenya at 4.30pm Monday.

Mwangi said he was told the appointment with immigration was to confirm that his application for an extended bridging visa had been accepted, but was also told to ensure his family remained at home.

“It was a set-up,” he said. “He could have told me: you are coming in to be detained.”

Documents seen by Guardian Australia state the appointment was for an interview regarding his application for a type-E bridging visa.

Instead, his wife, Semisha Mwangi, said, she and their young children went along to show support.

She is a Noongar woman and the couple married according to Noongar law in Narrogin – Semisha’s family’s traditional land about 200km east of Perth – in 2017, before marrying under Australian law at a ceremony in Perth in December.

She said John Mwangi is a devoted stepfather to her seven-year-old son, Clive, and co-carer with her to her sister’s three children aged one, three and 12 under an Aboriginal kinship care arrangement.

“That ripped me apart seeing him in handcuffs like a criminal, escorted out the back like a murderer,” she told Guardian Australia.

John Mwangi and his stepson, six-year-old Clive Kickett. Photograph: Supplied by family

She said she and the children visited him in detention on Sunday and were worried they would never see him again.

“My son keeps asking me: when is dad coming home?” she said. “I have almost given up, thinking that he is leaving today.”

John Mwangi came to Australia on a student visa in 2009 and was transferred to a bridging visa. He had been trying to apply for permanent residency.

He met his wife in 2015 and they have been living in a de facto relationship for almost four years, while he worked as a nursing assistant for a contractor servicing Perth’s major hospitals. He also supported her to return to work by helping with childcare.

Mwangi’s latest bridging visa expired on 7 February 2019, and he had filed the paperwork to extend the visa and also applied for ministerial intervention, writing that he was concerned their own children would be taken away by child protection if he was not here to support his family. Those applications were rejected.

“My wife is having a lot of difficulties trying to care for her sister’s children as well, but when there are two of us there it is much easier,” Mwangi told Guardian Australia. “I tried to explain that when I applied for ministerial intervention but they kept saying I didn’t meet the date range.”

John and Semisha on their wedding day in Perth in December 2018, two years after being traditionally married in a Noongar cultural ceremony in Narrogin. Photograph: Supplied by family

Semisha Mwangi says that the department has not accepted their traditional cultural marriage under Noongar law as the date of their marriage, and appears to believe the marriage in December was for immigration purposes.

“We have been married for two years,” she said. “It took two years to get financially stable and financially able to be able to afford the full wedding, and the rings, and get a beautiful dress and a tuxedo for Johnny.”

The couple have applied for urgent ministerial intervention to allow Mwangi to stay in Australia. Semisha Mwangi says she is concerned that her son and her sister’s children, for whom Mwangi is a positive male role model, will be badly affected if he is made to leave.

Family advocate Gerry Georgatos said Semisha Mwangi will be “in tremendous hardship without him”.

The Department of Home Affairs said it did not comment on individual cases.