Your answer to your questions is going to be found in the proceeding that has already taken place. The file in that probate case, as well as everything filed throughout the litigation, is open to the public. If you care to learn more about it, you might consider contacting your mother's attorney (assuming he or she will talk to you) or reviewing the file for yourself or with the assistance of your own attorney.
This answer does not constitute legal advice. I am admitted to practice law in the State of Texas only, and make no attempt to opine on matters of law that are not relevant to Texas. This answer is based on general principles of law that may or may not relate to your specific situation, and is for promotional purposes only. You should never rely on this answer alone and nothing in these communications creates an attorney-client relationship.
It sounds to me like maybe the court where the will was probated threw it out and considered your grandmother as dying intestate (without a will). In that case, its most likely that the court awarded the estate property to the "heirs at law" or your mom and her sisters. As my esteemed colleague suggested the best bet is to check out the file and then consult with a lawyer, either the one for the estate or another one in the court where the estate was opened. Good luck
Legal disclaimer: Donald J. Quinn II is a Missouri attorney. As such, his responses to posted inquiries, such as the one above, are limited to his understanding of law in the jurisdiction in which he practices and not to any other jurisdiction. In addition, no response to any posted inquiry should be deemed to constitute legal advice, nor to constitute the existence of an attorney/client or other contractual or fiduciary relationship, inasmuch as legal advice can only be provided in circumstances in which the attorney is able to ask questions of the person seeking legal advice and to thus gather appropriate information