There are some circumstances in which you might interpet the word "relatives" to exclude your parents and siblings. For example, if you normally live with your parents, and someone says to you, "Are you staying with relatives this weekend?", you might assume that they mean relatives other than the ones normally live with.
However, generally speaking, "relatives" includes your immediate family as well as more distant relatives. In fact, the person asking which relaive you resemble is more likely to have close relatives in mind than distant ones, if only because you're less likely to know whether you resemble a distant relative.
So, it's entirely legitimate to answer the question by saying you're like your mother or father. It's also entirely legitimate to answer it by saying you're like your aunt, uncle, grandfather, grandmother, cousin, or another relative of whom you have sufficient knowledge to answer the question.