Claiming German citizenship through Grandparents

I believe it's not possible, because based on German Law(if I am not mistaken) the citizenship of parents in the time a child was born is the deciding factor. I do know there are cases where the grandparents were German and the parents also (automatically) German but never registered as German bec. born and living abroad. In that case I believe its very possible for your friend to get this citizenship, even in the case of grand-grand parents, as long as no one in the line ever renounced it(not using it and not registering it doesnt meant renouncing it) BEFORE your friend was born. I believe your friend has a very weak case, however, perhaps a good lawyer may help(to dig into why his father was renouncing it, etc, maybe there is something that can be used to make a case. This is what I know. Hope that helps.

Not possible. If a child is born to a German parent then they get citizenship; not to one that has already renounced or on the basis of their grandparents. This has been covered in detail on many threads here. Just look at the Wikipedia page on German immigration law. And this is the standard situation for most countries. The only countries in Europe I know of that have a possibility through the grandparents, with multiple caveats, rather than strictly looking at the parents are Italy and Ireland. Seems to be a general myth that people can get citizenship based on ancestry.