These family legends often get exaggerated. The big thing in my family was that one of our cousins Wallis Warfield married the King of England who renounced her throne for her. I never did ever find out how close a cousin she really was but to hear my relatives tell it, she was almost a sister rather than a cousin. There was also a lot of talk that a great, great whatever was a prince, my estrangend grandfather was Jewish, that we have "black blood" in us. (we all have an overabundance of singing and dancing talent!)
I have no idea how much of these family legends are true. But I bet that Obama's relatives used the much more known location of Auschwitz when retelling the yarn.