This is a sticky situation to say the least. Since it sounds like your aunt is willing to work with you on this, I would give her every opportunity to do so. You do not want to sue her, and it is not entirely clear that you would win, if you did. So your best chance at straightening this out is really to help her to do what you want her to. If she refuses to do that, then you have a decision to make. It then depends on the value of the account and whether or not it is worth suing your aunt. If you get to that point, you will need an attorney to assist you.
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I agree with Mr. Frederick, if your aunt is performing, be patient. You may want to take the will and trust agreement to an attorney and have them review the documents and advise you on your rights if you feel that your aunt is truly not acting as she should. But if the credit union will only release funds to your aunt, then the account is probably payable to the trust.
The money belongs to your aunt as the beneficiary designation overrides the provisions in the will. You should bring all documentation to a probate/trust attorney for review and also consider the ramifications of causing friction within the family. It may not be worth it.
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