An inquiry into the Hills Shire Council has been searching for Jean-Claude Perrottet, Mr Perrottet's younger brother, for more than a week. However the 26-year-old has not responded.
Also wanted by the inquiry are Liberal Hills Shire councillor Virginia Ellis and her son, Christian Ellis.
Upper house Labor MP and committee member John Graham told AAP the committee hoped the trio would decide to report to the inquiry.
"We're calling on them to co-operate. We're calling on the public to report their whereabouts," Mr Graham said.
The inquiry intends serving summons on the three outstanding witnesses and has hired professionals to track them down.
The inquiry was launched after Liberal MP Ray Williams used parliamentary privilege to allege several senior Liberal Party members were paid to install people on the council who would be friendly to developer Jean Nassif.
The premier declined to answer questions on Tuesday about his younger brother's whereabouts after last week telling reporters to leave his family out of his political affairs.
"That's a matter for him," the premier said when asked why Jean-Claude had failed to answer the inquiry's requests.
The committee has previously heard Jean-Claude joined with Mr Ellis and asked businessman Frits Mare for $50,000 to branch stack the seat of federal Liberal MP Alex Hawke, a move that would see him removed from parliament.
Meanwhile, Education Minister Sarah Mitchell has accused her opposition number of misrepresenting the effect of merged classes and teacher vacancies during a 2GB radio debate.
While vacancies had doubled, half of schools had zero staff vacancies and another quarter had only one, she told Labor education spokeswoman Prue Car on Wednesday.
"You are constantly negative about it," the minister said.
"Do you think 2000 teacher vacancies is positive?" Ms Car fired back, prompting Ms Mitchell to ask what the number should be.
"You constantly peddle this myth that thousands of kids are learning without a teacher in the classroom and it's not true, it's a lie," the minister said.
The pair also clashed over the future of a COVID-19 school tutoring program, that's helping 350,000 of the state's 1.2 million students.
While the Liberals will extend the program at an annual cost of $173 million, Labor will shave it back to $100 million per year, with a particular focus on the under-performing year 10 cohort.
Ms Car said the government's extension was "just ... a sugar hit to get through the election".
"This is our third year of funding, it's not an eve-of-election sugar-hit. That's a lie," Ms Mitchell said.
Meanwhile Labor is promising to establish a contemporary music office called Sound NSW, modelled on the film office Screen NSW.
It's part of a $103 million investment in the contemporary music scene which includes a promise to bring back lost live music venues.
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