A professional server has travelled more than 1,900 kilometres to track down three Liberal members, including the NSW premier's brother, sought to appear before a parliamentary inquiry.

But Liberal factional figure Jean-Claude Perrottet, former Liberal state executive member Christian Ellis and his mother, Hills Shire Councillor and political staffer Virginia Ellis, cannot be found.

Two private firms were engaged by a New South Wales upper house parliamentary committee on Thursday to deliver the summons to appear before an inquiry into impropriety at the Hills Shire Council and property developers in the region. 

The parliamentary committee said they were "making a deliberate decision to avoid appearing before the committee" after staff were unable to find them to issue the summons.

Professional help was engaged, and almost a week later an update to the committee said that one server spent "in excess of 17 hours" in and around Deniliquin in the state's south-west.

They travelled to several rural properties as well as local pubs and RSLs in search of Christian and Virginia Ellis.

At one property, Christian Ellis's wife was home.

"The agents asked the female person, 'Is Christian Ellis home?' to which the female person relied 'No, he's not here,'" the report from Tim Tierney and Associates said.

The agent asked whether his wife knew when he would be home or how to contact him.

The report states she responded: "No, I don't know his movements. I do not know where he is. I am sorry I cannot help you".

"The agent noted the female person to appear nervous and evasive," the report said. 

On a separate occasion the professional server arrived at a property at 8:45pm and "noted a number of lights on inside the property".

"The agent approached the premises and heard voices inside the residence, however after doorknocking for a number of minutes the agent found the voices to cease," the report said.

"No person would answer the door."

The agent used a local contact who informed him that there was a possibility Mr Ellis was staying with another brother of Mr Perrottet, not one wanted to appear before the inquiry.

A second private firm, Sharmans, searched in Sydney for Jean-Claude Perrottet as well as Christian and Virginia Ellis.

The agent went to Mr Perrottet's office but was advised he was on leave, the report said.

They also visited a small farm in Sydney's north-west in search of Christian and Virginia Ellis, which had a locked gate and an intercom.

The report states the intercom was answered by a female who "sounded like a teenager" and told the agent: "They're both not home at the moment."

The parliamentary inquiry will resume on Thursday.

The hearing was called last week in the hope that the missing Liberals would have been located in time. 

"These witnesses are impeding the proper processes of parliament and this committee in exercising its inquiry power," the committee chair, Sue Higginson, said.

Charles Perrottet, who was also unable to be found to be summonsed but was believed to be interstate, made contact with the committee earlier this week.

In a letter he told the upper house MPs he would not be participating in the parliamentary inquiry, labelling it partisan and defamatory.

The inquiry was launched six months after the Liberal member for Castle Hill, Ray Williams, used parliamentary privilege last June to allege members of the NSW Liberal Party had been "paid significant funds" to install new councillors in the Hills area to benefit the development company Toplace. 

Toplace director Jean Nassif has previously written to the committee denying the allegations made by Mr Williams.

Former Hills Shire councillor Alan Haselden will give evidence to the inquiry.