I would say goto the one you like better from interview date. If you goto your second choice and really like it, that'll put you in more of a dilemma. In some sense, it's not too informative, but I enjoyed seeing familiar faces and unfamiliar faces so when school starts you'll be more at ease.
Edit: One more thing, plenty of people bring spouses, parents, and siblings. It's usually business casual and no ties required unless it's mentioned.