1. Registration of WILL is not compulsory. Even an unregistered WILL will have the same legal validity as that of a registered WILL. So, if the unregistered WILL mentions your name as the beneficiary of your deceased father's property, then it will be sufficient to mutate his property in your name.
2. The documents needed for mutating your name against your deceased father's property are death certificate of your father, WILL, family tree, sale deed and khatha/patta certificate.
3. It would be legally correct to sell the property to a prospective buyer only after your name is mutated against the property in the jurisdictional revenue records. After mutation has been done in your name, you can appoint through POA preferably, one of your blood relatives as Attorney/Agent to sell the property on your behalf.