What are my rights regarding inherited trust property?

Anyone can sue anyone; the question is whether the lawsuit has any merit. Your mother and aunt were co-trustees to a trust for your grandfather. Unless you became a co-trustee with your aunt by virtue of language specifically in the trust, your aunt really has no case. It is not your responsibility to handle your grandfather's wishes, and if you were willed items from your mother, those items have become yours and therefore, to do with them what you desired. If your aunt as co-trustee failed to ensure certain collectibles were donated, then she failed the trust as a trustee.  So if the historical society knew his intention and were informed of the collectibles and existence of the trust and the society's role as beneficiary, that historical society could actually sue your aunt for failing to protect the beneficiary's interest and obtain a personal claim against her. She is suing you because either a) she is already being sued or b) is preparing for that lawsuit to come shortly. She had three years (prior to your mother's passing) to ensure those collectibles went to their rightful owner. So, if you have a writing saying his wishes (donate or keep), that could arguably be referencing the trust and if it did specifically reference the trust, a good lawyer would indicate this was a clarification of the trust and should be incorporated by reference.