HOW TO HANDLE THIS SITUATION

You should immediately file a suit for declaration and injunction against transfer of any kind of the suit property. You your gandmother has left any moveable assets and alueables you can also file an application for succession certificate which should not take more than 6-7 months. If your grandmother has not transferred the suit property to the said person or any third person her legal heirs should not face much hurdles to get injunction and decalration.

Firstly a notarised document has no legal sanctity,enquire from society whether they have obtained membership basing on the said document if so issue a notice to the society?if they obtained permission from corporation for construction file objections to the same in corporation and  file a suit for injunction in the said suit array corporation as a defendant.succession certificate is not required as it is immovable property.It is only for debts and securities a Sucession certificate is needed to be obtained.U can as well seek a decleration that the property belongs to u(legal heirs of u r grand mother)