I think your question has been answered, but I just wanted to point out that the Yang Family Tree
posted elsewhere on this site was meant to clear up misunderstandings and answer just this sort of question.
"Yang" means "poplar tree" and is a common surname. In theory, surnames indicate descent from a common clan, but Chinese history is so long that many connections have become lost, entangled, or reinvented and only the less common surnames are likely to be taken at face value as evidence of common descent. "Yang" is probably equivalent to an English name like Carter or Miller.