Inheritance disputes are more likely to erupt when one child is given control of a family trust while siblings or other relatives also stand to benefit, a study of 640 contested trust cases has found.
The arrangement can combine sibling rivalry with a significant imbalance of power, particularly when the trustee has discretion over payments from the trust, according to the research published in the Washington University Law Review.
Christopher Ryan, a professor at Indiana University Maurer School of Law and one of the study’s authors, described the set-up as “an important recipe for conflict”. He said it could reinforce feelings that a parent had shown favouritism.
The researchers examined thousands of civil filings listed for hearings at San Francisco Superior Court between 2014 and 2020. Ryan carried out the study with Reid Weisbord of Rutgers Law School and David Horton of the University of California, Davis, School of Law.
Almost a quarter of the disputes involved one descendant beneficiary suing another descendant beneficiary who was also a trustee. Many of those involved siblings by blood or marriage, although some petitioners may have been grandchildren.
Almost all the cases concerned revocable trusts, which can allow a successor trustee to manage a person’s assets after their death. Trusts are commonly used to avoid the time and expense of probate, but the cases showed they can also lead to prolonged and costly family litigation.
The average dispute lasted 481 days, including cases that were settled. In 74% of petitions, trustees were accused of misconduct, most commonly a breach of their duty of care or loyalty.
Nearly one in three beneficiaries sought a detailed account of the trust’s finances. David Horton said that suggested some beneficiaries believed trustees were mismanaging money or taking funds improperly.
However, the researchers said financial concerns were not always the main force behind the disputes. Horton pointed to the case of the Mar siblings, whose trust’s cash assets were exhausted during litigation that continued for more than five years.
Raymond Mar, who died in 2016, gave his son the right to live rent-free in his home for the rest of his life. A disagreement over whether the son could take in a tenant led the siblings to court.
In 2024, a judge criticised both sides for excessive litigation and ordered the trust to be dissolved and the property sold. Raymond Mar’s daughters nevertheless filed in October 2025 to have their legal fees deducted from their brother’s share.
People who challenged trusts generally fared poorly when disputes proceeded without settlement, the study found. Petitioners were 48 percentage points less likely to win or settle when a case required a formal trial rather than being decided by a judge on written filings and oral arguments.
“A petitioner who is hellbent on getting everything they want due to emotional reasons is less likely to compromise or recognize that their case is flawed,” Horton said.
The researchers estimated that up to three-quarters of petitions ended in settlement. The precise proportion was uncertain because about a third of cases disappeared from the court docket without a ruling on their merits, although the authors believed many had been settled.
Mediation appeared to improve the prospects of resolving trust disputes. Some 85% of cases that went to mediation ended in settlement, compared with 47% of those that did not.
The authors advised parents to address difficult estate-planning decisions with relatives while they were still alive and to consider appointing an independent or professional fiduciary.
Horton said: “Death brings out strong emotions. It may be a good practice to explain your estate planning choices to your loved ones while you’re alive to flush out any conflict.”
Ryan also warned that parents should not assume clauses designed to deter legal challenges, including provisions that disinherit beneficiaries who contest a trust, will prevent court action. Their effectiveness varies between states, he said.
“I would plan for conflict rather than assuming drafting can eliminate it,” Ryan said.
