People who might have claims include those who are beneficiaries of the will, heirs of the deceased, or creditors of the deceased. For instance, in California there are certain requirements to disinherit children or a spouse. If these requirements are not met, then a child or spouse may be eligible to receive a portion of the estate despite being omitted from the will. Additionally, inheritance disputes are focused on the language of the will and whether the property can be distributed according to the will; they are not focused on the validity of the will.
The best way to determine if you have a claim is to look at who are the beneficiaries and what property is distributed. For example, if your parent gifted their car to you but the will provides that the car goes to a different beneficiary, you may have a claim to the car. Obviously, the best scenario is if you can come to an agreement with that beneficiary which would then only require court approval.