Validity of the ownership title of commercial shops

My father bought two commercial shops approx 170 square feet from the seller in 2007 and seller executed a Notarized GPA in favour of my father without paying stamp duty and registration fees containing agreement to sell ,will,receipt .At the time of purchase the seller was also holding the notarized GPA from the first seller who has the title of ownership in the registrar office.My father passed away in 2010 before her demise my father executed a notarized family will in favour of my mother.My doubt is since supreme Court judgement came in 2011 October that notarized GPA is not a valid instrument for transfer of immovable property title or ownership but it was optional before that we are looking to sell the property to the buyer by executing a registered sale deed in subregistrar office.What validity will that sale deed hold and will subregistrar raise any questions about the legality of ownership of my mother.I have a chain of notarised gpa with me .what are the various options available to me ?The property is located in narela-110040 Delhi.Only ground right.