Is the house not part of my father’s estate and already belongs to my sister because she has lived in it for so long?

My father passed away last August. He owns property with 2 homes on it. He lived in 1 my sister in the other. My sister has lived in the other home for approximately 30 years. She claims that the house is not part of my father’s estate. That it is "grandfathered" because she has lived there so long it is hers. My father left a will which he had me read prior to his passing and it did not state specifically who got what, he just left everything to his children. The same sister has the will at this time and will not let anyone see it or have it to start probate process. Is she right on the house matter?