It is the worst kind of choice: does Patricia Goossens lose her Belgian husband and their family’s only guaranteed source of income, or does she abandon her home in Scotland and leave her autistic adult daughter behind?

Her husband, Frans, is disabled and receives invalidity benefit payments from the Belgian government after contracting peritonitis in 2006, a debilitating abdominal infection that left him in a coma. That whole income of about £200 a week will stop, the Belgian authorities have told them, if Britain leaves the EU without a deal on 30 March.

In theory, the couple could claim benefits in the UK – Patricia might be entitled to a carer’s allowance and Frans could potentially claim for a personal independence payment.

Yet Frans cannot apply for settled status until after Britain leaves the EU, on the day the Belgian government would stop paying his disability benefit. And there is no guarantee that the Department for Work and Pensions (DWP) would assess him as disabled.

The uncertainty means that they will have to make a decision before Brexit day. If they leave, Patricia’s 34-year-old daughter Alice, who has Asperger’s, will stay behind because of the costs involved in arranging for a passport for her, Goossens said.

“I could stay put and lose my husband, who is disabled and needs me, and I love him and don’t want to be parted from him,” Patricia told the Observer. “But when I go with him, I lose my daughter, whom I also love and who also needs me.”

The couple met in 2007 when Patricia, who is a proud daughter of a Highlander – “a famous poacher”, she said – was still making a living as an animal hide tanner. They married in Ullapool in 2012, and Patricia gave up work to look after Frans and Alice at the family’s cottage in Balchrick, a tiny township on the tip of northwest Scotland, where salt winds from the Minch strait batter the coastline.

The idea that there might be any problem with Frans’s benefits only occurred to Patricia last year, and she contacted RIZIV, the Belgian government’s health and disability insurer that pays Frans his income.

An official from the Belgian federal public service for social security replied in November that when the UK became a third country “invalidity benefits can no longer be exported”.

“Your husband will therefore no longer receive any disability benefits from the Belgian social security system, based on current legislation,” the official wrote. “To continue to benefit from them, he would have to settle in Belgium or another member state of the European Union.”

Patricia contacted her local MSP and the Scottish government to ask for help, but since benefits payments are a national matter, they could only point her towards the DWP.

“Neither I nor my husband cost the UK government a penny,” Patricia said, adding that his medical needs are covered by European insurance from his Belgian disability benefit. “We have always been reluctant to apply to the DWP for Frans, purely because his disability is ‘on the inside’, if that makes sense.” A DWP spokesman said anyone in difficulty should call the helpline or visit their local Job Centre.

If Frans were to apply for benefits, he would need to prove that he was settled in the UK and could apply for settled status. To do that now, he would need to buy an Android phone or travel to Edinburgh, 250 miles away. After 30 March, the process will become easier and he could send his documents to the Home Office. But by that time, his Belgian income would have been cut off.

“We have no financial buffer,” Patricia said. “People in our situation cannot afford to wait it out. Optimism alone won’t pay our rent or feed or keep us warm, should the worst happen.”

Even if Frans did get settled status, there is no guarantee he would receive any UK disability benefit.

The couple are now drawing up plans to move to Belgium and stay with Frans’s relatives until they find something permanent, but taking Alice with them is not an option. She has no passport and an application may mean travelling more than 100 miles to Inverness for an interview and an overnight stay – something that is beyond their means.

Patricia said her landlord had been “fantastically kind” and had agreed to let Alice stay. They are trying to arrange housing benefit for her. “But she will be very isolated here. And though she is actually reclusive and needs a lot of solitude, she also needs her mum and stepdad, and I don’t know how she’ll cope for long without us. That’s one of our major worries. But I’ll fight to keep my family together and us in our home till the very last day.”