sister spoke on Tuesday of her pain and confusion at UK Foreign Secretary response to her brother's imprisonment.
Egyptian-British dissident sister Sanaa Seif addressed a press conference in the British parliament on the 74th day of her brother's hunger strike, saying he was "slowly dying" but "wants to live".
She said there was a "window of opportunity" to save him but that her family's loss would be "huge" if he died.
"We're deeply puzzled by the way we have been treated by the foreign secretary, Liz Truss," Seif said.
"Why hasn't she met with us 'til now? Why has she still not made an official statement about Alaa? I can tell you it hurts."
Seif added that she believes Egypt has been rejecting the UK's requests for consular access to Abdel-Fattah because if they "see the state he's in" they will "act with more urgency".
During the press conference, British-Egyptian actor Khalid Abdalla announced the launch of a letter he said urges Liz Truss to "use her power to secure Alaa's immediate release".
The letter is backed by over 1,000 celebrities and cultural figures, including Judi Dench, Riz Ahmed, Angela Davis and Stephen Fry.
Abdel-Fattah, 40, a blogger and hero of the 2011 Egyptian revolution, is serving five years in jail for "broadcasting false news" after he shared a Facebook post.
Rights groups denounced his trial as unjust and Amnesty International considers the computer programmer, who was convicted in December after being held for over two years, a prisoner of conscience.
Abdel-Fattah was previously imprisoned between 2013 and 2019 and was not out long before being rearrested.
His family announced they had secured British citizenship for him through his mother in April.
Seif on Tuesday raised the possibility Abdel-Fattah could be freed in exchange for him renouncing his Egyptian citizenship and being deported, which she said he is willing to do.
Abdel-Fattah's other sister, Mona Seif, recently began a hunger strike of her own in solidarity with her brother.
"On Sunday, my sister visited Alaa in prison," Sanaa Seif said.
"When she saw him, she was shocked. She hasn't been able to eat since. She told me, 'I have to use my body as a portal to show people what's happening to Alaa.'"
Meanwhile, the son-in-law and daughter of James Fitton, 66, who is imprisoned in Iraq for attempted artefact smuggling, also addressed the meeting in a pre-recorded video.
Fitton received a 15-year sentence following what his daughter Leila called a "highly political, unfair and ridiculously harsh verdict".
She described the items as "tossed-aside archaeological debris" and said he had been "actively encouraged" to take them as "souvenirs".
Sam Tasker, Fitton's son-in-law, criticised the UK's response to the retired geologist's case.
He said: "We have been frustrated beyond our wildest imagining by the complete lack of compassion and empathy displayed by junior ministers in our case and by the complete lack of engagement by the foreign secretary herself.
"The foreign secretary has, to our knowledge, never even acknowledged Jim's existence."
He urged an "open and frank public conversation" about the role of Britain's Foreign, Commonwealth and Development Office (FCDO) as a "guardian and advocate for citizens facing injustice and human rights abuses abroad".
"We believe there is a vast gulf between the public's expectations of the support you will receive in these circumstances and the actual experiences of families like ours," Tasker said.
Rich Parry, a friend of ex-BBC cameraman Peter Jouvenal, who is being held by the Taliban in Afghanistan, felt similarly.
He said he has "very grave misgivings about the FCDO and what they're doing".
Others in attendance included husband Richard Ratcliffe, Liberal Democrat MP Layla Moran and Labour lawmaker David Lammy, the MP for Abdel-Fattah's sister Mona.
In response to a request for comment from °®Âþµº, an FCDO spokesperson said: "The UK government continues to raise Alaa Abdel-Fattah's case at the highest levels of the Egyptian Government.
"We are working urgently to secure consular access to Mr Abdel-Fattah. We are also concerned by reports that he is on a sustained hunger strike.
"The welfare of British nationals in detention remains a high priority."