Unregistered sale

My mother sold multi tenanted property belonged to her father in 1982. As of today the said sale deed is not registered. 7/12 extract, Name on the property card is still on my grand fathers name. Recently I changed  my grand fathers name and inserted my mother and my name on the property card as well as 7/12 extract

Now my question is can I claim this property back?  Whats the procedure? At present I have duel nationality.

Property is in Thana Dist. Maharashtra