You mother's Will needs to be probated in the county and state where she last resided where the superior court of the county and state in this country will then issue an order as to whom is to receive the assets and property of your mother located in Mexico. Once obtained, a certified copy of the order is then sent to the county and state in Mexico recorder's office for recording in order to transfer title to who was gifted the real property.As to assets in Mexico that are not real estate, perhaps retaining a Mexican attorney for assistance in the transfer of such per the United States court's order.