Regarding will creation and stamp duty to be paid for registration

I have an unregistered will of our property in the name of my wife, who is already died. The will is in my name n prepared around 2002. I want to transfer this property in the name of my 3 children so:- 1) if I create new will, do they need to pay any stamp duty to register this to transfer in their name after my death? 2) Also the unregistered will be valid or should the registration of will is mandatory?