Is it permissible to withdraw money from the account of a sick mother who cannot control her urination and suspects her children, to buy a burial plot for her without her knowledge?

The default rule is the impermissibility of disposing of another's property without their permission. The mother's illness does not permit guardians to dispose of her property unless her condition has reached a state of mental incapacitation (ataha). Guardianship over the mother's property is not valid except through a testament (wasaaya) or from an authorized entity. It is permissible for the guardians of a mentally incapacitated person to dispose of their property in a way that serves their best interest. Purchasing a burial plot is considered to be in her best interest if there is no free public burial plot available.