Earlier quoted context omitted.
In Germany, the obligation to pay alimony depends on the child's income. Only when the childs income (before taxes) excceeds 100,000 Euros per anno she/he has to pay something. There exists no obligation to pay alimony for grandparents.
What if you're estranged from your parents? If you haven't talked to them for twenty years are you still liable?
Just a side note: If someone has received gifts from a person who later becomes destitute, he or she must return the gift under certain conditions (the gift was made no more than 10 years ago, the recipient was not destitute on his or her part, it was not a gift of decency such as a small birthday or Christmas present, etc.).
[1] BGH, Judgment of 12 February 2014, Az. XII ZB 607/12 (PDF, in German) http://juris.bundesgerichtshof.de/cgi-bin/rechtsprechung/doc...