Whether or not you have a claim or case will depend on a wide variety of factors that will determine your standing and the strength of your claim. Only certain people can contest a will, litigate a trust, or obtain a guardianship or conservatorship. For more specific advice for each area you can read our other articles on the subject.
As a brief overview, in order to have standing to sue for a will or trust you must be either a beneficiary of the will or trust or have certain powers for a trust. For a guardianship or conservatorship, you must be a government agency, a government employee, or an interested person like those for a will. In other words, you generally need to have some sort of relation to the person you are petitioning for guardianship over.