Is it permissible for the mother to dispose of the father's money, while he is afflicted with Alzheimer's, in such a way that most of it goes to the brother, and the sister is deprived of it on the pretext of her marriage, knowing that the father was just among his children?

The power of attorney becomes void if the principal loses his sanity, as in the case of Alzheimer's. Consequently, the mother is not entitled to dispose of the sick father's money based on the previous power of attorney, whether through gifting, charity, or managing his real estate. All such dispositions are legally invalid.