Is it permissible for children to dispose of their father's property, he being afflicted with memory loss disease, in order to spend on the household and some of themselves, and to invest the surplus funds?

The loss of reason necessitates placing the individual under guardianship, while their ownership remains. They are prohibited from disposing of their wealth until they recover. If a person who has lost their reason is placed under guardianship, a guardian must be appointed over their wealth. This guardian is obligated to preserve and grow the ward's assets. Expenditures from the ward's wealth are made in a reasonable manner for those whose maintenance is obligatory upon them, and the zakat on their wealth must be paid.