Someone could always contest a will. Whether they will be successful is another question. As a general rule, if there is a written will that was properly witnessed, the challenger has a hard task.
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Any beneficiary can contest a will. But the success or failure of that challenge is very fact-dependent. You need to consult with an experienced attorney.
This answer is provided for informational purposes only, is based upon the limited facts provided by you, which are assumed to be true and accurate. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.