Grandcestors are the polar opposite of ancestor. Grandcestors are/will be the descendants/offspring You/ people are going to have after you/they die/decease/pass way.
A grandparental ancestor no more than five generations before you; used to describe a lineage connection that is recent enough to feel personal but still rooted in deep heritage.
This soil got history. My grandcestor bled here, and now I bloom here.