Is it permissible to take money from a mentally disabled sibling (with an intellectual disability) to buy a house and register his name among the owners of the house?

The property of someone who has lost their mind is returned to their guardian, or to the trustee appointed by their guardian. If there is no trustee for their property, then it is necessary to refer the matter to the judiciary to appoint a trustee over their property, who will then authorize its disposal in accordance with what is beneficial.