Kahui has denied murdering the two three-month-old boys Chris and Cru who died on June 18, 2006, within about 14 hours of each other at Auckland Starship Hospital after they were admitted to Middlemore Hospital on June 13.
Macsyna King, 31, said that on the evening of June 11, 2006 she had gone out with her sister, against Kahui's wishes and ended up at his father's home.
She said she fell asleep on a double bed in the lounge with her son Shane and Kahui's younger brother Elvis, when she was woken up about 11pm by Kahui who was angry, she said.
Kahui yelled at her to "get my arse up and get my arse home," she said.
"He was boiling, irate, angry as..."
Ms King swore at Kahui to go away and that she would "do what I wanted to do".
She said she told Kahui to get "his own arse back home" to look after the boys and that she could not believe he had left their children in the care of her brother and his partner at their south Auckland home.
Ms King returned to her home the next morning and said she fought with Kahui again when she told him she was going out again.
Kahui did not want her to go out and accused her of just wanting to get drunk, she said.
She swore at him and said she was going whether he liked it or not, she said.
The twins were in the "best condition" when she left and was not worried about them, she said.
Ms King spent the night at her sister Emily's house and found out the next morning that Cru had apparently stopped breathing for a while.
Ms King arrived back at their house about 20 minutes before Kahui and checked on the twins, who were both sleeping.
She noticed Chris had a fresh bruise on his face, she said.
When Kahui arrived at the house Ms King said she "had a go at him" and asked "how the hell did our baby get the new bruise and what the hell happened".
Kahui said he had left the boys in the nursery but had not closed the door and their son Shane had crawled into the cot and "got at the boys".
Ms King said she accepted the explanation from Kahui.
Kahui said he had been holding Chris in the nursery and called out to his sister Mona, who then noticed Cru's lips were blue, she said.
Ms King did not feed or bathe the children that morning because they were sleeping and Kahui said he had not fed the twins during the night.
Ms King decided to go to their family doctor to have the babies checked, with the family stopping at McDonald's on the way, during which the twins continued to sleep.
Apart from the bruise on Chris and being told of Cru's breathing problem the previous night, Ms King said she did not notice anything unusual about the twins.
Dr Gopinath Nayar examined the boys in their carseats, and Ms King spoke of his look of "shock".
He said he was concerned about the boys and they needed to go to the hospital.
Ms King said she could not remember what Kahui's reaction had been.
She told the court earlier today that Kahui was a caring and loving father and that she was the dominant partner who sometimes became violent towards him.
"I would yell the loudest, I would swear at him. I just wouldn't stop until I got my way to be honest."
Ms King said she would sometimes get physical, including kicking him in the shins and slapping his face.
Kahui was a quiet softly spoken person but would bottle things up until he would "really lose it", she said.
As a father, Kahui was careful and loving with their eldest child Shane and their twins, she said.
She will continue to give evidence tomorrow.
