1. It is not mandatory to have a will registred.
2. In most of the places, Will is required to be probated but such grant of probate is not mandatory if the property is situated at Delhi.
3. Whom did your said Aunt bequeathed her properties to?
4. The said beneficiary is the absolute owner of the said property of your late Aunt and he/she shall have to execute and register a gift deed in favour of your father.
5. The other legal heirs of your late Aunt should sign the said Gift Deed as witnesses.
6. It will be prudent on you part to get an Affidavit executed and registered by all the legal heirs of your Aunt affirming that they are aware that the demised Aunt has executed a will in favour of someone for which they have no objection or grievance and do not wish to contest the said Will.
7. Stamp duty will be based on the value of the property being transferred.