Partition on self-acquired property

Hello Everyone, This is a self acquired property(house) by my grandfather. I am requesting clarification on behalf of my father. My grandfather has 5 sons & 4 daughters (9 heirs). His elder son and a daughter died. Elder son died before my grandfather died(in the year 2005). At the time of house construction, his elder son has helped his father(my grandfather) with an X amount. On exchange, he has got signature from my grandfather (which he was unaware) for half of the property. The property was registered in the year 1978 under his elder son's name. Now in the year 2019, elder son's son claims that he wants to demolish and build a new house for him, in the place registered for his father. Please clarify below: 1. Is the deed registered valid(though my grandfather was unaware)? Can we confirm if this is not forged, by any means? Can we file a law suit on him? 2. Does he need signature from rest of the heirs, in order to change from his father's name to his name? 3. If we divide rest of the property, do we need give a share to elder son's son OR can we divide among 8heirs? 4. If he is okay not to get a share on 2nd half of the property, do we need to get his signature on NOC or any documents required stating he will not object anything in future? 5. Do we now need to register the 2nd half of the property from our grandfather's name to rest of the heirs? 6. According to the general rule passed by Supreme court on 2 Feb, 2018; married daughters are eligible to get equal share on father's property even father has deceased before the year 2005. Please confirm if this correct. Thank you.