Prosecutor Alexandra Bull described the crimes as "physical abuse, sadistic punishment, emotional abuse and neglect".
The siblings remembered numerous episodes of cruelty at the hands of their father, they told the court.
They described being forced to hold up placards reading the word "liar" and being beaten and whipped with a belt.
The daughter also recalled being made to write "I am a liar, I am a stealer" 1000 times on paper, before being "whipped" by O'Brien.
The daughter told the court she begged for them to stop while they cut her hair, but she said her pleas were "worthless".
In another incident O'Brien "bashed" his son's head repeatedly against a wall after he downloaded games on a phone while the couple had been away. The court was also told the boy was told after having his own head shaved "it was a sign he was a liar".
The son was also not given food, and was prevented from using the toilet - instead having to use a bottle in his room.
The children were also forbidden from having friends by both parents, who deleted numbers from their phones.
The children both engaged in self harm, and O'Brien poured vinegar into their open wounds. The court was told their father told them, "that will be a lesson not to self-harm again".
During a police interview O'Brien told officers his son was "manipulative and a pathological liar". Both parents later admitted their roles in the abuse.
Sentencing Judge Nigel Daly said children had been victims of "gratuitous degradation".
O'Brien was jailed for 26 months on Wednesday. Mrs O'Brien was given an eight-month jail term suspended for 18 months.
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