One Estate-Planning Mistake That Turns Families Into Courtroom Enemies

A new study of 640 inheritance disputes reveals why putting one child in charge of a family trust often sparks legal wars between siblings.

When a wealthy parent dies, the fight over their money can get ugly — and a new study shows exactly which choices trigger the worst family battles.

Researchers analyzed 640 contested trust cases filed in a San Francisco court between 2014 and 2020. Their findings were published in the Washington University Law Review. A trust is a legal arrangement where someone (a "trustee") manages money or property on behalf of others (the "beneficiaries") — often used to pass wealth to family after death.

The single biggest cause of conflict? Choosing one child to control the family trust while their siblings also stand to benefit. Experts call this "a recipe for conflict," because it mixes normal sibling rivalry with a real power imbalance — and can revive old feelings that a parent played favorites.

Key findings from the study:

Nearly 25% of disputes involved one family beneficiary suing another who was also acting as trustee.
74% of cases accused the trustee of misconduct, such as breaching their "duty of care" (the legal obligation to act responsibly).
The average case dragged on for 481 days — over a year.
Around 75% of cases ended in a settlement (an agreement reached without a full trial).

One example: the Mar siblings burned through all of their trust's cash and spent more than five years in court fighting over whether their brother — who was allowed to live rent-free in the family home — could take on a tenant.

Emotion, not money, often drives these fights. The study found that people who refused to settle usually lost. Petitioners' chances of winning dropped by 48 percentage points if their case went to a full trial.

The researchers' advice to parents: talk openly about your plans while you're alive, consider hiring an independent professional to manage the trust, and don't assume clever legal wording will prevent fights. Notably, 85% of cases that went to mediation (a guided negotiation) settled, versus just 47% without it.

The bottom line: plan for conflict, because families rarely handle inheritance calmly.

This is an AI-generated summary. Read the original article at: https://www.cnbc.com/2026/09/25/study-estate-planning-heirs-legal-battles.html