Here you should be clear on this with your family prior to the interview if you think there is a chance it may come up. Do not say yes just to get the job if the real answer is no. This can create a lot of problems later on in your career. Be honest at this point and save yourself future grief. Confidence and enthusiasm go a long way even if your answer is a "Maybe" or "No," so don't count yourself out of the running if you cannot relocate.