Don Baxter, the former executive director of the Australian Federation of AIDS Organisations who was awarded an Order of Australia Medal this year for his services to the community in the prevention of HIV, has taken his case to the Supreme Court in a bid to get a greater share of his father's estate.

Mr Baxter, 64, who is retired and lives in a million-dollar two-storey terrace house in Darlinghurst in inner Sydney with his partner Rob Holland, is suing his brothers, Bill, 67, former minister for roads and ports in the Kennett government, and Stewart, 61, who were the executors of their father Allen's estate.

Allen Baxter died in January 2011, aged 96.

In an affidavit filed with the court, Don Baxter said he received $50,000 from his father's estate which was valued at $576,590.

But Mr Baxter said he believed his father had disposed of almost all of his wealth before his death to his two brothers and their children.

He described how his late mother, Mavis, one of nine children from a small farm, died on March 8, 2008, at the age of 86 at Nathalia Hospital in northern Victoria leaving an estate of $2.32 million.

Mr Baxter said in his affidavit that he only received $50,000 from his mother's estate but did not make a claim for more money at the time "because I was reluctant to interfere and cause family disruption and I expected I would be provided for out of my father's estate when he passed away which I believed to be many more millions of dollars".

Mr Baxter remembered his father showing him a list of shares he owned in November 2008 worth $6.684 million, including over $1 million worth of BHP shares.

The Baxter family also owned large tracts of land in north central Victoria.

Mr Baxter claimed the size and nature of his father's estate was complicated by the "lack of clarity" about the role of Baxter Family Trust and the Baxter Family Property Trust and what property and assets they owned, as distinct from his father.

The trustee of the family trusts was William McAteer Pty Ltd, whose directors and shareholders were Bill and Stewart Baxter and Stewart's wife Wendy.

Several parcels of land had been transferred in and out of the trust over time, Mr Baxter said.

He claimed his relationship with his family had had its ups and downs but he remembered visiting the family farm at Picola in about 1986 with his partner, Rob Holland, after he had come out as a gay man and his father warmly welcoming Rob.

"They found common ground by discussing Holden utilities from the 1960s (which Rob collected) and welding machines," Mr Baxter said.

Outlining his financial position when giving evidence in court on Tuesday, Mr Baxter said he and Holland owned the Darlinghurst terrace house they lived in worth an estimated $1.1 million to $1.2 million; he owned a studio apartment in Surry Hills worth between $260,000 to $300,000; and had almost $500,000 in superannuation.

Mr Baxter said his brother Bill had a substantial parliamentary pension and significant assets, including a home on the Murray River near Wahgunyah and a terrace house in Carlton, but it appeared significant land holdings had been transferred into Bill's name.

"I believe that my father has also transferred his very significant share portfolio to family members other than me before he died," Mr Baxter said.

"Based on the land transfers and the fact that Bill has handled much of the financial affairs for the farm, I believe he has received a sizeable proportion of the share portfolio my father showed to me in 2008 as well."

Mr Baxter believed his brother Stewart had received a substantial income from the farm and had received a sizeable share portfolio, as well as significant land holdings transferred into his name.

He claimed the support and assets provided to his brothers and other members of the family were more extensive than the $9000 loan and a $2500 1967 Toyota Corona his father had given him.

The civil trial, before Justice Kate McMillan, continues.