I am a little confused. If you know that you are beneficiaries, then you must have a copy of the Trust. If that is the case, then the only real question is whether or not the trust was "funded." By that, I mean, did the trust have any assets titled in it? If so, then you are right to petition the court and have her explain why she has not properly administered the trust.
If you do not have a copy of the trust, the situation is a little less clear. It is possible that you are not beneficiaries at all, in that case, and that you may not be entitled to a copy, depending on your relationship. Heirs would be considered interested parties of the trust, but it is not clear whether you would be considered an heir or not, without knowing more about the surviving family members.
If there are no assets in the trust, it does not matter what the trust says. It would only apply to assets titled in the trust. If the trust says I leave everything to my great niece, and all of the assets are titled jointly with the trustee, or name the trustee as the beneficiary (in her individual name), then the trust does not apply.
You may not be able to practically determine this without going to the court. Unfortunately, it could be expensive, if you need to go that route. You do not mention if you know your aunt's attorney or not. Presumably, he or she drafted the trust and may be able to give you some or all of the information you need. I would try to contact the attorney before you do anything else.
Having the trust document is only part of the battle.
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I agree with Atty. Frederick and would add that there may be options that you have not considered. It would be wise to talk to an attorney about the details of your issue.
Most firms, including my firm, offer a free consultation. Take advantage of it!
Please let me know if I can help further.
Its a relatively simple process..
Write a letter to the trustee asking for an accounting of the trust
Hire a local attorney (before or after the above)
The attorny can file a motion for an accounting and to remove the successor trustee in the probate court in the county where your aunt lived. That will start the process.
Answering this question with general knowlege of the law does not create an attorney client relationship and attorney cannot be held responsible for how the questioner uses this information.