Overall, your odds of successfully challenging a family member's or loved one's will are low. Judges are inclined to respect the wishes of the decedent (known in legal terms as the testator) if the will was properly prepared according to state law.
However, courts have been known to void all or part of a will based on a challenge. The most common successful challenges involve a decedent's testamentary capacity (the ability to understand the consequences of the will's provisions) and claims that the decedent was unduly influenced by one or more people in writing or changing a will.
Adults are assumed under the law to have testamentary capacity. Specifically, they are expected to understand what a will is, the value of their property and the identity and relationship of the beneficiaries whom they've listed.
To challenge a decedent's testamentary capacity, a person must provide evidence that when the testator created the will, he or she was suffering from dementia, lacked mental capacity, was under the influence or was mentally ill.
Another common reason for challenging a will is when family members believe that the decedent was manipulated or threatened into leaving assets to someone, such as a caretaker or romantic interest, rather than to family members. Claims of undue influence often go hand-in-hand with those involving lack of testamentary capacity. People who are suffering from dementia, for example, may be tricked into changing the terms of their will without realizing what they're doing.
Other potential reasons to challenge part of a will include provisions that are illegal, the lack of sufficient witnesses and, of course, evidence of a more current will.
Sometimes a family member will challenge a will based on the residence of the decedent. As long as a will is valid in the state where the decedent's permanent home was, it is considered valid in whatever state the person died in and can be settled there.
If you believe you have grounds for challenging a loved one's will, it's best to seek the guidance of an estate planning attorney. He or she can help you determine whether you have sufficient grounds to make a successful challenge.
Source: FindLaw, "Reasons to Challenge a Will," accessed March 21, 2018