e.g. "I am going to my aunt and uncle's house." or "I am going to my aunt's and uncle's house." If it's one house, belonging to two people. I am inclined to think the former, but want to double check.
Rumwriter, The first one. I just made a blog post those goes over all this if you have any other questions about possessive nouns (or Nouns in general, to be honest).
