A Sydney charity has been accused of cashing-in on its severely disabled clients, with documents suggesting it may have been double-dipping on rental payments.

Key points: Parents said the charity was claiming rent from pensions and the Government

Parents said the charity was claiming rent from pensions and the Government All up the charity was claiming three times market value in rent

All up the charity was claiming three times market value in rent Sylvanvale said pensions were used to pay for various living expenses

Parents of three young men with intellectual disabilities have spoken out over concerns about a residential group home run by a not-for-profit called Sylvanvale.

The parents have obtained documents using Freedom of Information laws that suggest the charity may have been double-dipping on the rent.

While it is not illegal, the parents said the charity had been claiming rent from both the men's pensions and the NSW Government, adding up to more than $130,000 a year.

Vanessa Browne said Sylvanvale had been asking for $81,000 a year from four clients' Disability Support Pensions for rent, food and bills.

Documents show the charity was getting at least $52,000 a year "rental component" from the Department of Ageing, Disability and Home Care on behalf of the residents.

That means, once food and bills are subtracted, the charity has been collecting about three times market value in rent.

Mary Lou Carter, whose son Nicholas lives in the Carlingford home, said she had hired a forensic accountant to audit her son's finances to no avail.

Sylvanvale's Carlingford group home in north-west Sydney. ( ABC News: Dave Maguire )

"I believe my son is being ripped off," she said.

Vanessa Browne discovered the funding anomaly when she applied for paperwork about her son.

"Sylvanvale has been very disappointing," she said.

Sylvanvale supports about 600 people in 50 locations around Sydney.

In a statement, a Sylvanvale spokesman said it paid its landlord $36,000 a year in rent.

It uses the men's pensions to cover that rent along with food, bills, utilities, repairs, maintenance, vehicle use and upkeep.

He said the other $52,000 rental component was flagged during the initial tender process but was ultimately "consolidated" into its ongoing funding for day-to-day care and to supplement household costs.

"We are a not-for-profit service provider and securing and allocating funds to provide the best possible services for all our clients is paramount," he said.

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Ongoing fight for group home sitting empty

The concerns of double-dipping are the latest development in a dispute between three parents of residents in the Carlingford home and the State Government.

The group home at West Pennant Hills parents say was purpose built for their sons. ( ABC News: Kathryn Ward )

They have accused bureaucrats of reneging on a 2012 promise to give their sons a purpose-built group home.

The house at West Pennant Hills in Sydney's north has been built and sitting empty for three months.

The State Government has told parents the clients can only move in if they stay with Sylvanvale.

This is because one lot of parents out of four clients in the home who were promised the house want to stay with Sylvanvale.

Sylvanvale said the families had rejected the new house and a third option on the Northern Beaches.

The families said they had indicated they would accept the new house and the Northern Beaches house is not even built.

The State Government said it would investigate the claims made.

A history of unexplained injuries and sedation

The three parents from the Carlingford home want to sever ties with Sylvanvale because of concerns about safety.

Vanessa Browne's son Alex, 22, has a rare genetic disorder.

Alex Browne's mother says he has suffered unexplained injuries. ( Supplied )

"The main problems have been the lack of safety, lack of supervision, low staff ratio and pressure to sedate," she said.

"There have been so many unexplained injuries."

Mary Lou Carter's son Nicholas, 25, is severely disabled from a chromosomal condition.

She was outraged when Sylvanvale staff had her son arrested after he lashed out while being ill, then staff were told not to call her.

"My chief concern is the lack of qualified staff," she said.

Bernadette Moloney, whose son Charles shares the same condition as Nicholas, said her son had also sustained unexplained injuries while in Sylvanvale's care.

Charles Maloney had unexplained bruises around his neck. ( Supplied )

"I discovered bruising all around his neck, his chest, his back and his left shoulder."

In a statement, Sylvanvale said it could not comment on individual cases.

"We can provide assurance that we have acted appropriately and within the required guidelines," a spokesman said.

"Legislation is in place to ensure that such matters are reported and investigated by the NSW Ombudsman.

"The care of our clients, sometimes amidst challenging circumstances, always comes first."

The Department of Family and Community Services said it took all allegations of abuse and neglect seriously and would investigate.

Ms Moloney said their situation did not bode well for the full roll-out of the NDIS.

"I am sick of all the banter about person-centred care when it's not person-centred at all.

"It seems to be the service provider gets the priority."