Ancestral property is inherited property that has been passed down through at least four generations of a family, specifically within the male lineage.
It is distinct from self-acquired property, which is purchased or earned by an individual using their own resources.
For property to be considered ancestral, it must remain undivided across those four generations.
In your case the property has not passed through the next generation of your great grandfather.
Your grandfather is alive and he has rights to succeed/inherit the property along with his siblings and once they divide the property among themselves, the property becomes the individual's self acquired property after the said partition.
The concept of four generations is that it should not have been divided after the death of each generation male lineage, whereas in yor case the grandfather is still alive and had been enjoying the property as a successor in interest, hence it will not fall under the ancestral property category.