Eh, even if you count it, it should half for each step removed from you, as the non-existant grandchild’s other parent will still have a child, just with someone else rather than with your child.
It’s like saying that killing someone 1000 years ago will also kill all their descendants, which is technically true. But most of the descendants will still live, just one different parent (grandparent, etc).
System wide ad blockers can’t block a lot of ads, namely same-domain ads or those that are built into the html. Much rarer than the external page kind (DNS ones) thankfully.