Lindt siege victim Katrina Dawson's family criticises "outrageous" police decision.

The families of Lindt Cafe siege victims Tori Johnson and Katrina Dawson have criticised police and the DPP days before inquest findings into the attack.

In an interview with the ABC’s Four Corners, the families also questioned the influence of a psychiatrist, who had thought Man Haron Monis didn’t want to kill.

Police stormed the Martin Place cafe in the early hours of December 16, 2014 after Monis shot dead Mr Johnson 17 hours into the siege.

Monis, 50, was shot dead by police and Katrina Dawson was fatally wounded by at least seven police bullet fragments.

Katrina Dawson’s brother Angus Dawson said a decision that police would only enter the building if a hostage was seriously injured or killed was “staggering”, while Jane Dawson, his mother, called it “outrageous”.

“They shouldn’t wait for (the captives) to be impacted on in any way, they should be saving them from death or serious injury,” Ms Dawson said.

Mr Johnson’s mother says she can’t “forgive people” for the decision.

"I'll never be able to understand... how you can make a calculated decision that you wait for someone to die," Rosie Connellan said in an interview aired on Monday night.

"It's just beyond me."

Sandy Dawson, Katrina's father, said the unidentified psychiatrist brought in to advise negotiators appeared to have a great deal of influence.

"They certainly influenced the negotiation cell because he was supposed to be just an advisor to the negotiators," he said.

"In fact, it seems that he was a lot more than that."

NSW Coroner Michael Barnes will on Wednesday hand down his findings into the December 2014 siege sparked by Monis, who faced charges relating to the brutal murder of his ex-wife and dozens of sexual assaults.

"The fact that the DPP didn't oppose bail (in October) was extraordinary," Sandy Dawson said.

"But what was even more extraordinary was they tried to have any consideration of bail excluded from the inquest."