Not sure how much Pete is being serious and how much he's just entertaining himself playing the 'who can be the bigger victim' game, so, let's just take it at face value;
If the grandparents can be held responsible, why not the great grandparents? There's plenty of them alive these days. And if them, why not the great, great grandparents? All dead and gone? Just establish what was inherited from them and go after that?
Run on sentence ahead; I would argue that too many lawyers arguing that someone else is responsible for X/Y/Z etc is one of the core problems with our society in the first place and, based on that, I would argue against going back in time and creating a whole new level of responsibilities and it would certainly require all sorts of lawyers in order to argue cases, for and against, where this grandparent is better than that parent and thus gets custody which then leads to the OTHER parent coming back on the scene to not only argue THEY are now the better parent because they got their life together but that now some OTHER grandparent who had nothing to do with this owes them money to help raise the child 'properly' and yet another generation of kids is taught to view the world ever more cynically.
Talk of this kind all leads back to one place; the village. Run by the government.