Depends on what you mean by "both names." If the title to the property is held by them as "joint tenants" with right of survivorship, then the interest of your grandfather passed automatically to your grandmother and all she has to do is file a document with the county recorder certifying his death. If the property is held as tenants in common, then each of them own a 50% undivided interest in the whole property. Some sort of court proceeding (depending on the value of the property) has to happen to transfer his half. If he died intestate it probably passes to his spouse. I suggest you check how title was held and if necessary consult local counsel on what to do next.
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