In December 2014, self-styled Islamist Man Haron Monis held 18 people hostage inside a Lindt cafe in the city centre.
Heavily armed police stormed the building 17 hours later after Monis shot cafe manager Tori Johnson.
Relatives of Mr Johnson and Katrina Dawson, who was also killed, said police had put their lives in danger.
The families said they were shocked by revelations at an inquest that police had planned to intervene only if the gunman killed or injured someone.
“I’ll never be able understand how you can make a calculated decision that you wait for someone to die,” Mr Johnson’s mother, Rosie Connellan, told the Australian Broadcasting Corp (ABC).
New South Wales coroner Michael Barnes will hand down his findings into the 18-month inquest on Wednesday.
Monis was shot dead by police during the raid, while Ms Dawson, a barrister and cafe customer, was killed by stray bullet fragments fired by police.
The inquest aimed to establish whether deaths were avoidable and if it should have been treated as a terrorist event.
Ms Dawson’s family said the police tactics were “outrageous”.
“The idea that we had to wait for somebody to be killed or seriously injured before the police would act was staggering,” her brother, Angus Dawson, told the ABC as part of a documentary to be aired on Monday.
The barrister’s mother, Jane Dawson, said: “They should be saving them from death or serious injury.”
Zinn, said he had lost faith in police because of their “great level of incompetence” during the incident.
It is the first time the families have publicly criticised police, aside from when Mr Johnson’s parents stormed out of the inquest during one testimony.
Questions about why police snipers did not attempt to shoot Monis were heavily discussed during the inquest. [/restrict]