Sibling Rivalry: What Happens When a Sibling Disputes a Parent's Will

What is a will contest?

A last will is a legal document that isn’t easily overturned. If your sibling contests your parent's will, they must prove specific legal grounds—such as lack of mental capacity, undue influence, fraud, or improper execution—for a court to overturn it.

Just because your sibling decides to contest the will doesn’t mean they’ll actually overturn it.

Who can contest a will?

Under probate law, wills can only be contested by people with legal standing, including:

• Spouses
• Children
• People mentioned in the will or a previous will

When one of these people notifies the court that they believe there is a problem with the will, a will contest begins. Your sibling can't have the will overturned just because they feel left out, it seems unfair, or because your parent verbally said they would do something else in the will.

A last will and testament can only be contested during the probate process when there is a valid legal question about the document or process under which it was created.

How to contest a will

A last will and testament is presumed to be valid by the probate court if it is in the proper format. Codicil to a will can only be contested for very specific legal reasons and the process begins when an interested person notifies the court.

There are only four main legal reasons a will can be contested:

1. Improper execution. Execution is all about how the will is signed and witnessed. If your parent signed it and there are two witnesses and all of your state's requirements are met, there is no problem. If the signature is not of your parent or a witness didn’t actually sign it, then there could be questions about its validity.
2. Lack of mental capacity. One of the most commonly argued reasons for a will contest is that the testator (person signing the will) did not have testamentary capacity. This doesn't mean your parent needed to be 100% mentally together—in most states, the standard requires that your parent understood their assets and what they had to give away, knew who their heirs and beneficiaries were, and evaluated the effect of the will (even people in the early stages of dementia can meet this standard)
3. Fraud. If your parent signed the will as a result of fraud, it is not a valid will. An example of fraud would be someone handing them a document, assuring her it is a health care proxy or real estate contract and having them sign it when it was actually the will.
4. Undue influence. A will is invalid if the testator was unduly influenced at the time of signing. A common example is a full-time caretaker who has taken complete control of an elderly parent's assets, decisions, and day-to-day life, influencing them to sign a will that might not reflect what the parent really wants.

What happens after a will is contested?

If your sibling actually contests the will or codicil and the court agrees that a will is invalid, it may reinstate an earlier will, distribute assets according to state intestacy laws if no prior will exists, or uphold part of the will while interpreting how the remaining estate should be distributed.

When a sibling files a contest, probate essentially freezes—no assets can be distributed until the dispute is resolved. Contesting a will is expensive and time-consuming as it typically takes six months to several years, depending on the complexity of the case and court backlogs. During this time, the estate pays legal fees to defend the will, which reduces the inheritance available to all beneficiaries.

Legal fees for will contests commonly add up substantially, depending on whether the case settles or goes to trial. The contesting sibling bears their own attorney costs, but the estate typically pays for the executor's legal defense. Both sides may go through extensive discovery, including depositions, document requests, and expert witness testimony.

In practice, most contested wills never reach a final court ruling. The majority are either dismissed for lack of evidence, settled through negotiation (often with the challenger receiving some portion of the estate to end the dispute), or resolved through mediation. Full trials are relatively rare because both sides recognize the cost and uncertainty involved.

How to prevent a sibling from contesting a will

While you can't completely eliminate the risk of a will contest, there are several strategies that can significantly reduce the likelihood of a successful challenge. These preventive measures work by addressing the specific vulnerabilities that make wills contestable in the first place.

1. Include a no-contest clause 

Also called an "in terrorem" clause, this provision states that any beneficiary who contests the will and loses forfeits their inheritance entirely. For this to be effective, the potential challenger must stand to lose something meaningful—if your sibling was already disinherited, a no-contest clause won't deter them. Some states also limit enforcement of these clauses when the challenger had probable cause to contest.

2. Document testamentary capacity 

One of the strongest defenses against a lack-of-capacity claim is evidence that your parent was mentally competent when signing. This can include:

• A medical evaluation conducted close to the signing date
• Video recording of the will signing ceremony
• Detailed notes from the attorney about the testator's demeanor and understanding
• Testimony from credible, independent witnesses

3. Work with an experienced estate planning attorney

Wills prepared by attorneys are often harder to challenge than because they're more likely to meet all technical requirements and include protective language. An attorney can also identify potential conflict points and address them proactively—for example, including a brief explanation in the will for why distributions are unequal.

4. Consider a revocable living trust

Assets held in a trust pass outside of probate, which means they generally aren't subject to the same contest procedures as wills. Trusts also offer more privacy since they don't become public record, reducing the information available to a potential challenger.

How to resolve inheritance disputes with siblings

Not every inheritance conflict needs to end up in court. Alternative dispute resolution methods can save money, preserve family relationships, and reach faster outcomes than litigation. Before committing to a lengthy legal battle, consider whether these options might work for your situation.

Mediation

Mediation involves a neutral third party who facilitates discussion between siblings to help them reach a voluntary agreement. The mediator doesn't make decisions but guides the conversation toward resolution. Many probate courts now require or strongly encourage mediation before allowing a case to proceed to trial. Mediation typically costs a fraction of litigation and can resolve disputes in days rather than months or years.

Sign off family settlement agreements

Family settlement agreements allow all heirs to voluntarily agree to distribute the estate differently than the will specifies. If everyone with an interest in the estate signs off, the court will generally honor this agreement. This approach works best when siblings can communicate openly and are willing to compromise.

Arbitration

Arbitration is more formal than mediation—an arbitrator hears both sides and makes a binding decision. It's faster and less expensive than court but removes some control from the parties involved.

When attempting any resolution, focus on interests rather than positions. Your sibling may be demanding a specific asset not because they want that item, but because it represents something emotional—recognition, fairness, or connection to the deceased parent. Understanding the underlying interests can open creative solutions that litigation can't provide. An estate attorney or professional mediator can help facilitate these conversations, especially when grief and family history make direct communication difficult.

What is the success rate of contesting a will?

Most wills are upheld by courts. Successful contests require substantial evidence of legal grounds such as lack of capacity, undue influence, fraud, or improper execution—emotions alone aren't enough.

Only a small fraction of wills are ever contested, and of those challenges, very few result in any change to the estate distribution.That change might mean full invalidation of the will, but more often it means a negotiated settlement where the challenger receives a portion of the estate to drop the case.

Success rates vary significantly by the grounds for contest. Claims based on undue influence and lack of mental capacity tend to have higher success rates because they often involve observable patterns of behavior and medical evidence. Fraud and improper execution claims are harder to prove and succeed less frequently.

Several factors increase the likelihood of a successful challenge:

• Strong documentary evidence, such as medical records showing cognitive decline
• Recent changes to the will that dramatically benefit one person
• Evidence that the testator was isolated from family members
• Multiple credible witnesses who can testify to the testator's state of mind
• A prior will with substantially different terms

Some siblings threaten a will contest when they feel slighted or hurt and don’t ever follow through. Before pursuing a contest, consider the cost-benefit calculation carefully. Even with reasonable odds of success, legal fees may exceed the potential recovery—especially for smaller estates or when the contested portion represents a modest increase in inheritance.

Brette Sember, J.D., contributed to this article.