Aicha Dahane, a Napier University graduate from Leith, is desperately worried about Brahim, a prominent human rights activist. He was arrested six months ago, after visiting Western Saharan refugee camps in Algeria.
The group of six prisoners has now refused food for 26 days, asking either to be released or given a date for a trial. Mr Dahane has already spent four years in prison, where he claims he was tortured.
Now MSPs Shirley-Anne Somerville and Linda Fabiani are supporting Ms Dahane's campaign for their release, and calling for the UK Government to put pressure on Morocco to do so.
Ms Dahane, 35, was forced to flee her home country after protesting about the Moroccan occupation of Western Sahara. She is now a British citizen and has made a new life for herself in Leith, completing her degree in information technology last year.
Her brother has travelled around the world as president of the Saharawi Association of Victims of Serious Human Rights Violations Committed by Morocco. But he was arrested in last October, and since then has been held without trial.
Ms Dahane said: "They are now really suffering from the hunger strike. He is seriously ill and already has heart problems and stomach ulcers. But he is willing to go on until death.
"I'm so worried about him now. I don't know how I can manage if anything happens to him.
"I heard from my family this week and he is really weak now. They are all in wheelchairs and he says he cannot feel his left arm any more. It is unfair and unjust for them to be kept without fair trial."
Mr Dahane was accused of working with an "enemy of Morocco" after visiting the refugee camps. But his sister says other human rights groups have visited recently, without facing arrest.
She said her family were reluctantly supporting his hunger strike, although they are all desperately worried about him. As well as eight siblings, he has a wife and three-year-old son.
Ms Somerville, who represents the Lothians for the SNP, said: "I will be writing to the Prime Minister asking him to intervene directly in this case. This is a clear case of human rights abuse.
"It's unimaginable what Aicha and her family have been through. She is an amazing lady and very inspiring, but obviously gravely concerned about her brother."
Amnesty International is also calling for the prisoners' unconditional release.
Malcolm Smart, director for the Middle East and Africa, said: "We are increasingly concerned for the health of these detainees. We consider them prisoners of conscience imprisoned for the peaceful exercise of freedom of expression."