Furious relatives of the Indigenous man David Dungay Jr, who died in custody in New South Wales, have confronted guards outside his former prison on the second anniversary of his death.

The 26-year-old diabetic was three weeks away from being released on parole when he was restrained and died in Sydney’s Long Bay prison hospital in 2015 during a dispute about eating biscuits.

His grieving family is now waiting for an inquest into the matter, which will be held next July.

They marched with supporters to the entrance of the prison on Friday, with Dungay’s angry younger relatives yelling at several guards through the closed prison gates.

“Send them out, the eight who were involved,” yelled his nephew, Paul Silva.

“How would your family feel? I can’t even fucking sleep.”

Dungay’s mother, Leetona Dungay, demanded to know why she had been told there was no CCTV footage to show whether her son was OK the day before the altercation.

“Watch your children,” she yelled to several visitors waiting at the entrance to see inmates. “This is what they did to my son.”

Dungay said every time she attended a march or rally it stirred up grief but being at the prison on the second anniversary was especially tough.

“Once I get through the coroner’s court and get justice, I’ll feel much better,” she said.

Dungay wants to see more safeguards in all prisons to make sure deaths in custody are stopped. “Our people aren’t sent in there to be apes and animals and treated unfairly,” she said.

“That goes for every nationality – we all deserve to be treated like a human being, not like an ape. We’re not guinea pigs for them.”

A NSW Corrective Services spokeswoman said the commissioner, Peter Severin, “deeply regrets” Dungay’s death.

The commissioner and the department’s Aboriginal strategy and policy staff have met with Dungay’s family to “discuss their concerns and provide support” the spokeswoman said.

She said the department had been conducting a thorough investigation into the death but could not comment further because of the impending coronial inquest.

Last month the deputy state coroner Derek Lee scheduled a a 10-day inquest for July and acknowledged the Dungay family’s patience had been tested.