Twin brothers born in London and brought up in state care could face deportation to two different Caribbean countries they have never visited.
Siblings of Darrell and Darren Roberts, 24, said they had been issued with deportation notifications and could be put on planes when released from jail for grievous bodily harm.
Darrell’s lawyer said his client was British and had served his sentence.
The Home Office denied it had issued a deportation order.
“Neither Darrell or Darren Roberts are currently detained under immigration powers nor are they subject to deportation orders,” a spokesman said.
“The Home Office considers carefully all cases where an offender is suspected of being potentially liable for deportation and it has a particular responsibility where the offending is prolific or high harm.”
But the BBC has seen a notice sent to one of the men that indicates the Home Office does intend to pursue deportation.
The twins were born in west London to parents from the Caribbean islands of Dominica and Grenada, with neither parent having UK citizenship.
They were taken into care by Ealing Council’s social services at the age of 13 when their mother died and their father returned to Dominica.
Darrell was sentenced to a six-year prison sentence for grievous bodily harm at the age of 17.
His family said on his release he was served with the deportation notice to the Dominican Republic, a country he has no connection to.
Darrell believes officials named it in error because his father was born on the island of Dominica.
His twin Darren remains in prison on a separate sentence for grievous bodily harm.
According to his family Darren has been warned he faces deportation to Grenada – the country where his mother was born – when he finishes the jail sentence.
The Home Office automatically issues a deportation notice to anyone without citizenship who has been convicted of a reasonably serious offence with a sentence of more than 12 months.
Children born in the UK to parents who are foreign nationals can be eligible for British citizenship but are not automatically citizens.
Neither their parents nor social services applied, leaving Darrell and Darren technically stateless.
Freya Valie Roberts, one of the twins’ sisters, said she was “disgusted, upset and insulted” when she heard they were being threatened with deportation.
“If they’re going to deport my brothers, I mean there are 11 of us in total, they could pick and deport any one of us,” she said.
She said she was scared of what would happen to them in a country they had never visited and said they were being “just sent to a place and you’re not allowed to come back”.
Darrell’s lawyer, Andrew Sperling, compared what was happening to the twins to the 18th and 19th Century practice of penal transportation, where convicts were shipped to countries such as Australia.
He said Darrell was British and had served his sentence in “a society which apparently believes in rehabilitation and supporting people to reintegrate into the community”.
“This is what should be happening with this man. But instead, he’s having to fight a complex, terrifying legal procedure,” he said.
Family members have launched a petition to gather support for the twins, who they say should be able to remain in the UK indefinitely.
A spokesman for Ealing Council said its children’s services team had “repeatedly engaged with both Darren and Darrell” to allow them to apply for immigration status.
But he said “neither of the young men signed the documentation to allow it to be progressed”.
“We always work with young people to secure their status as part of the pathway planning process,” he said.
“Care leavers in Ealing are supported practically and financially to get the advice and support to progress their applications and any subsequent appeals they may make.”