Is it permissible to transfer the ownership of an elderly father's property, when he cannot distinguish right from wrong, to one of the children, to prevent his wife from seizing it, while guaranteeing her right to inheritance?

There is nothing that guarantees the stepmother's right when the property is registered in the name of one of the brothers, as this brother may seize the inheritance. To remedy this, the father can be placed under interdiction if he cannot distinguish right from wrong, or he can be persuaded to divide his current wealth among all heirs so that ownership transfers to them and each party feels secure.