It was unclear which child was shot first, but Ellen died from a single shotgun wound, while three discharges were apparent from Bradley's wounds.
Earlier that day, Livingstone had a supervised visit with the children at Barnardos in Dunedin.
It was to be the last of his six scheduled visits.
Barnardos receptionist Donna Rowe said Livingstone seemed normal during the hour-long visit, although he did inquire if there was to be another supervised visit as he had left a prior one early with illness.
"When he left his visit on January 15 there was nothing I could see that indicated what he was going to do later that night," she told Chief Coroner Judge Deborah Marshall.
Mr Croudis said before that visit Livingstone had purchased beer and cigarettes from a supermarket and filed a prescription for his antidepressants at a pharmacy.
Following his supervised visit with the children he visited BP Mornington and purchased petrol, including an additional quantity in a red plastic petrol canister.
Later that night, he took the shotgun and petrol canister to Ms Webb's Kiwi St home.
Livingstone entered Ms Webb's bedroom first, startling her and sending her fleeing from the house.
He then shot the children before becoming involved in a confrontation with neighbour Christopher Foot.
He shot at Mr Foot but missed and then it appears he turned the gun on himself.
Yesterday, the duplicity of Livingstone emerged at the inquest.
The inquest heard Livingstone deceived his psychiatrist, Dr Christopher Wisely, during their clinical contact.
Livingstone became estranged from Ms Webb after he brutally raped her in May 2013.
He attributed his actions to the antidepressant and smoking cessation drug Zyban.
Dr Wisely said he accepted Zyban was a factor in Livingstone raping his wife.
Many of the witnesses spoke about how Livingstone blamed his feelings and thoughts on the medication.
But his GP, Dr Coleen Lewis, was not convinced the drug contributed to his behaviour.
"It's not consistent with my experience and I see that it would be considered a very rare side effect to have psychotic behaviour," she said during her testimony.
Livingstone contacted her by telephone in August 2013, requesting Dr Lewis write a letter saying she prescribed him Zyban.
The phone call implied he was blaming the rape of his wife on the drug, she said.
She was so concerned by the implication that she contacted Dr Wisely and left a message, but he never replied.
Earlier in the day, a witness spoke of her concerns about Livingstone's behaviour towards Ms Webb and Ms Webb's neighbour, Melanie Foot.
Livingstone was "obsessive" about his estranged wife, the witness, who cannot be identified, said.
His behaviour had caused concern for the witness.
"He puts the s***s up me to be honest," she said. "It was nothing he said or did, it was just his manner."
Mr Croudis' testimony will continue this afternoon.
