Taking the opposite approach of movie favourite The Castle's Darryl Kerrigan, who rallied his neighbours to stave off developers, the residents have taken control of the sale process and are selling all their properties in a single transaction.

The move has been prompted by the rezoning of the area under the NSW government's Urban Activation Precinct plan and the development of the new Metro rail station opposite the Castle Hill showgrounds.

The Castle Hill deal will reap the individual owners as much as $4 million, substantially more than the average Hills district price of around $1 million.

The residents' appointed spokesman Nick Maude said the deal was struck when the neighbours were told of the rezoning about a year ago.

Mr Maude said it was an "emotional time" but that his neighbours were resolved to approach a commercial agent to sell the 25 sites in one line.

"We all started talking amongst ourselves and quickly realised we needed help," Mr Maude said.

Mr Maude said that when everyone was agreed, the group approached JLL and its head of metropolitan sales and investments for NSW, Sam Brewer and director, David Mathews, for help and guidance.

The increasingly common tactic of Sydney neighbours banding together to sell directly to developers and commercial agents is starting to hurt the local real estate agents who would have traditionally been enlisted to market and sell the properties individually.

In Castle Hill, 20 neighbours in an area adjacent to Mr Maude's group combined their lots in a single sale in July last year.

High profile agent John McGrath's recent financial troubles have been in part blamed on a big drop off in listings in areas like Castle Hill. Mr McGrath blamed his company's recent share price slump on the way the decline in listings in areas like Castle Hill, Epping and Kellyville had affected his Smollen Group agents.

The site being sold by Mr Maude and his neighbours is located at 3-7 Ashford Avenue, 17-39 Middleton Avenue and 12-28 Partridge Avenue and has potential for high density residential development, allowed by the new Hills district planning rules.

The whole site measures about 24,093 square metres with a potential gross floor area of 55,415 square metres.

"This site offers three strong factors setting it up for success," JLL's Mr Brewer said. These included its proximity to the Sydney Metro Northwest station that is planned to open in the first half of 2019. "The fact that it is the metro rail is key as this will offer trains approximately every four minutes during peak times, greatly improving connectivity," Mr Brewer said.

"It has proximity to retail and commercial precincts with Castle Towers and the Norwest Business Park close by.  We expect to see strong interest from local and offshore developers who are actively seeking opportunities of this scale in the market."

Mr Maude said the age of vendors ranges from people with small children to retirees in their 70s.

"Some people have invested in renovations and others have been here for 35 years, so it hasn't been an easy process," he said.

"But at the end of the journey, we feel we have more power as a collective than trying to stay put and being built out by the proposed high density developments."

Mr Maude said he had a child at high school and was keen to stay in the area, but said that others were contemplating a total change of lifestyle and location.

"The romance of staying, such as Darryl Kerrigan in the movie the Castle, is a lot different to reality," he said.

"We knew we had to leave, but we have the power to at least generate good returns through combining the properties."

"This is one the last remaining sites of this size in Castle Hill that is in such close proximity to the planned Sydney Metro Northwest train station at Showground Road. Castle Hill is experiencing growth with increased demand from families and young professionals. Infrastructure developments will further strengthen Castle Hill's position as a destination for residents in the future," Mr Matthews said.