Because the house is a public house, the ownership of the house cannot be inherited, and whether the right to use can be inherited can be determined according to the provisions of laws and local regulations. Grandchildren can inherit grandpa's house, but they must be given the right of inheritance through a legal and effective will.

First of all, Grandpa suffers from Alzheimer's disease, and is legally a person with limited capacity for civil conduct. He has no ability to make a will, so his will is invalid.

Secondly, grandma can exercise the right to make a will instead of grandpa, because she is grandpa's spouse and the first-order guardian, and the house belongs to the joint property of husband and wife. Grandma will exercise the right to make a will instead of grandpa, and she will also exercise the right to make a will, dispose of part of her property and leave the house to her grandson.

Third, the will must be legal and valid. In order to ensure its validity, it can be notarized by a notary office. A notarized will can take precedence over other forms of wills.

Fourth, after a will has a legal and effective form, it becomes legally effective. After the death of the two old people, the house will be inherited by the grandson, and the opposition of grandparents' daughters is invalid.