You can create a unifying theme if your chosen themes accommodate one another. Think about this: your spouse wants an Asian theme, your teenage daughter wants a gothic theme and you want a tropical theme. In such varied combination you may elect to do an around-the-world theme as part of your living room; this is like a miniature version of Disney's Epcot. You could potentially incorporate Asian tropic plants, samurai and dragons swords that would incorporate all three themes. The point is, regardless of the themes, there exists common ground that can be found.