Stalling a final decision on Bali Nine prisoner Andrew Chan’s plea for mercy may be the one hope of saving him and fellow prisoner Myuran Sukumaran from the firing squad, the pair’s lawyer says.

Julian McMahon said while Chan’s application for clemency to Indonesian president Joko Widodo was still unresolved, it remained the one critical point of negotiation for the Australian Government in its current high-level talks with Indonesia.

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“There’s no urgency to resolve it,” Mr McMahon said.

“And my hope is the question can be tackled in full with great care by Foreign Minister Julie Bishop and the Prime Minister in their dealings with the Indonesians.”

Sukumaran is not among the first group of six prisoners due to face the firing squad this Sunday, but on Thursday he was named as one of 16 prisoners, from a total of 64 on death row, who had been denied their pleas for clemency by the Indonesian president.

Chan’s chances of a reprieve appear equally doomed after president Widodo also made clear there was no prospect he would show mercy for any of the other prisoners on drug convictions.

Mr McMahon conceded the bid to save the two prisoners’ lives would be an “uphill battle”.

He said if Chan’s clemency application could be deferred – perhaps indefinitely – Sukumaran may also be spared because of the requirement under Indonesian law that prisoners who commit a crime together must be executed together.

Mr McMahon said if the Abbott Government could buy time more for the two Australians, it may also help persuade the Indonesian president that Chan and Sukumaran have genuinely changed during their time in prison and have also had a “remarkably positive influence” on fellow prisoners.

“I have real confidence that the more [president Widodo] learns about their rehabilitation the more he will be prepared to have another look at this situation.”

In the past week, a group calling themselves the Mercy Campaign have launched a desperate 11th hour bid to try to mobilise public support for the Bali Nine pair.

Professor Greg Craven, the vice-chancellor of the Australian Catholic University, said until now Australians had largely ignored the plight of Sukumaran and Chan because it was not a reality.

The scheduled execution of six men by firing squad on Sunday, he said, meant Australians would now have to contend with a “deeply confronting” execution process in which prisoners were robed in white, taken to a remote location, marked on the heart with a target and fired at by officers under express orders “to explode the heart”.

Professor Craven said it was crucial the Australian public ramped up efforts to send a clear message to Indonesia.

“The attitude of Australia and Australians will be become part of the reason why these men are executed if we are not sending the right signals to Indonesia,” Professor Craven said.

“If we do nothing, we are literally standing behind the firing squad.”

Professor Craven said the Abbott Government also needed to send much stronger signals to Indonesia about the damaging consequences for the relationship between the two countries if the two Australians were executed.

He said the Australian Government had made clear they did not want the executions to happen, but had stopped short of warning of the long-term rift it would inevitably cause once two “Australians are blown apart”.

“When we [get] to the point when we end up with social media with smuggled pictures of two Australians tied to a stake riddled with bullets – does anyone really believe that’s going to help our relationship?”