A Hunter Valley man and woman jailed over the torture death of a 12-year-old girl will plead guilty to their alleged roles in relation to the torture of the girl's surviving younger sister, a court has heard.

The dead girl's stepfather JK (names withheld for legal reasons) is serving a maximum 37 years in jail for murdering the girl, known as CN, in the Hunter Valley in 2015.

Key points: A Newcastle stepfather has been charged with the prolonged torture and repeated assaults of his stepdaughter

A Newcastle stepfather has been charged with the prolonged torture and repeated assaults of his stepdaughter The girl's mother has been charged with offences related to being an alleged accessory

The girl's mother has been charged with offences related to being an alleged accessory The court heard the girl was nine or 10 when she was allegedly assaulted

The girl's mother TP was jailed for a minimum of 18 months after a judge determined she had failed to protect her daughter from four years of assaults, failed to provide her with medical attention, and failed to alert authorities about the mistreatment.

The prior cases have been mentioned in Newcastle Local Court, as JK and TP had their matters heard in relation to the girl's sister NZ.

Charges were laid against the pair in relation to NZ earlier this year.

JK was charged with the prolonged torture and repeated assaults of NZ.

"Her untreated injuries have resulted in significant permanent scarring on her body and may have a significant impact on her future potential and lifelong career opportunities," court documents stated.

TP was charged with offences relating to being an alleged accessory to violence.

TP's solicitor Mark Ramsland today told the court his client had agreed to plead guilty to a lesser charge.

That charge is failure to provide the necessities of life by failing to take NZ to hospital.

JK's solicitor Sally Rostron told the court her client would also be pleading guilty, but the exact charges were being finalised.

Court documents allege abuse akin to torture

Documents for the case tendered in court said NZ was repeatedly assaulted in 2014 and 2015.

The documents alleged that JK subjected NZ to frequent serious assaults and behaviour that could be considered torture.

The documents said NZ was nine or 10 when she was allegedly assaulted, and was once picked up and thrown to the ground, fracturing her arm.

Documents alleged that in school holidays in 2014, NZ was assaulted for a three-day period.

The documents alleged JK made a hole in the back of a men's tie and placed steel balls in it before swinging it at NZ's back.

The tendered documents state weeping wounds on her back required eight months of daily treatment.

"NZ had to wear additional layers of clothing to cover the wound, which oozed fluids that were malodorous," the court documents read.

"This involved NZ wearing two school shirts and a jumper in spring and summer to prevent detection of the injury and therefore detection of the assault."

Police allege in the court documents JK also repeatedly slapped NZ on the cheeks and would hit her with a metal spoon.

Officers said as a result, NZ's face would become puffy and swollen to the point she was unable to eat.

TP and JK's cases are due to be heard again on November 14.