The family of an aspiring heart surgeon who was fatally stabbed have said they were treated “like criminals” by the courts and feel “let down” by the prosecution after a teenager was cleared of his murder.

Yousef Makki, 17, died from a single stab wound to the heart following an argument with a friend, known as Boy A, in an upmarket part of Greater Manchester on 2 March.

Boy A, 17, said he acted in self-defence and denied murder. He was found not guilty of both murder and manslaughter on Friday following a trial at Manchester crown court.

Makki’s family said on Tuesday they felt “traumatised” by the acquittals and were “back to day one” in grieving for the bright and popular teenager.

Makki was from a single-parent, Anglo-Lebanese family in the Burnage area of south Manchester and had won a scholarship to attend Manchester Grammar School. Just days before his death he had attended a talk on studying at Oxford or Cambridge universities.

Makki’s elder sister, Jade Akoum, 28, said the family had maintained their silence since March in the hope of securing convictions but they now felt obliged to speak publicly as they considered mounting a legal challenge against the verdicts.

“We will follow all the routes we can to fight this,” she said. “I’m not waiting for the Crown Prosecution Service to tell me because we put all our faith and trust in them before and they’ve let us down to be honest.”

Akoum said she felt the prosecution did not do enough to challenge Boy A’s claim that he acted in self-defence, and that jurors were left with an inaccurate picture of her brother because it focused largely on the day of his murder.

She said prosecutors had turned down an offer from Manchester Grammar School to provide a character reference for their former pupil.

The court was told of a row between Makki and his friends, Boy A and Boy B, also 17, following a botched attempt to buy £45-worth of cannabis in the leafy village of Hale Barns. Boy A was attacked, leading to a later confrontation with Makki. Boy A told the jury he pulled out a flick-knife because Makki had produced a knife – a claim denied by the victim’s family – and Boy A said he then accidentally stabbed his friend in self-defence.

Akoum said the family’s distress was made worse by the fact that they were made to sit in an upstairs public gallery during the trial, where they were unable to hear evidence and were surrounded by members of the public during often harrowing testimony.

Unusually for a murder trial, relatives of the defendants – both from middle-class Cheshire families – were given priority seating in the courtroom instead of the victim’s family. “We felt like the criminals the whole time. It felt like they [the defendants’ families] were the ones who were the victims,” said Akoum.

On the first day of the trial, Makki’s relatives left the court in tears when graphic footage of Makki’s bloodied body was shown without warning. Akoum said the family had to rely on a local newspaper website for live updates because they could not hear crucial evidence.

During breaks in evidence, Akoum said, the family were not provided with a private room and would often bump into the defendants’ families in the court. “We were so traumatised by what was going on – it should be private when we were seeing things we hadn’t seen before,” she said.

It is understood that Makki’s family have made a complaint to the court about their treatment but that it has not yet been resolved.

Akoum said she “felt the room spinning” when the not guilty verdicts were returned. The victim’s father, Ghaleb Makki, collapsed in tears after shouting “Where’s the justice for my son?” following the acquittals.

“The whole thing we’re not happy with,” Akoum said. “It’s infuriating for us because we just want the truth ... We feel that we’ve let Yousef down because we couldn’t even get him justice and like his life meant nothing to anyone else.”

She echoed the suggestion by Lucy Powell, the MP for Manchester Central, that jurors favoured white, middle-class defendants and that the result may have been different if the suspects were black teenagers from Moss Side.

“If it was the other way round – my brother is half-Arab and from a council estate ... [the verdicts might have been different],” Akoum said. “I think it went wrong right from the beginning. We kept quiet because we thought we were going to get justice at the end. Now we’ve got to speak up.”

Boy A was acquitted of murder and manslaughter. He admitted possession of a flick-knife and perverting the course of justice by lying to police.

Boy B was cleared of lying to police about what he had seen but admitted possession of a flick-knife. Both were cleared of conspiracy to commit robbery before Makki’s death. The two boys will be sentenced on 25 July for the charges they admitted.

• This article was amended on 19 July 2019. An earlier version stated that Hale Barns is in Cheshire. It is actually in Greater Manchester.

• This article was edited on 23 August 2019 to amend details relating to Boy B.