Undivided common interest

When my father died in 1987, he left my mother a “one-half common undivided interest” to all real estate owned by him at his death. My mother passed in March of this year (2021) and left one parcel of his real estate to someone not related to him. My mother never did anything with the property while she was alive. In fact, a title search shows that my FATHER’S name is still on the property. Can my mother leave this property to someone at all? If so, does it have to be someone related to him? In his will, my father left this tract to his son, my half-brother.