All the complainants have name suppression.
He denies pushing then kicking his ex-wife on their driveway after a night of drinking in the months before their marriage unravelled.
His ex-wife was eight weeks pregnant at the time, the court heard.
A few days later he drove her to hospital as she suffered a miscarriage.
The officer allegedly assaulted his nephew in the back of a police car after he ran away from home.
He was off-duty at the time and went looking for him in a police car with another officer.
"[The nephew] came back in a really bad way, beaten up and unconscious," said the officer's ex-wife.
"I had [him] lying down on the floor in the lounge and I was, at one point, trying to see if he was alive and conscious.
"[My ex-husband] was almost proud of himself for being able to bring [him] back to the property.
"He was laughing ... about putting him in the back of a police car and giving him the hiding of his life."
The officer was "embarrassed" of his nephew because of the nephew's run-ins with the law, his ex-wife said, and thought it was his role to "correct that".
On an earlier occasion he grabbed his nephew by his neck and pushed him up against a wall after he played a prank on his uncle, she said. The boy was aged 12 or 13.
The police officer spent time in state care as a child, along with his sister, the court heard.
He is also accused of psychological and physical abuse over a prolonged period of time towards his ex-wife's son, in his "formative years", amounting to one charge of child cruelty.
The stepson became a "selective mute" and withdrawn as a result of the alleged abuse, which included having his ears grabbed and being forced to say he had sex with a cat.
The officer has denied the allegations since they were first raised with police in 2009.
His lawyer Mark Ryan suggests the complaints have only arisen again recently because the defendant and his ex-wife are in a custody battle over their son, and it's a "tit-for-tat regime".
He said it would be "flawed thinking" to assume the male is the aggressor.
The trial before Judge Pippa Sinclair continues.
Where to go for help or more information
• Women's Refuge: Free national crisis line operates 24/7 - 0800 REFUGE or 0800 733 843
• Shine, free national helpline 9am- 11pm every day - 0508 744 633
• It's Not OK: Information line 0800 456 450 www.areyouok.org.nz
• Shakti: Providing specialist cultural services for African, Asian and Middle Eastern women and their children. Crisis line 24/7 0800 742 584
• Ministry of Justice: www.justice.govt.nz/family-justice/domestic-violence
• National Network of Stopping Violence: www.nnsvs.org.nz
• White Ribbon: Aiming to eliminate men's violence towards women www.whiteribbon.org.nz
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