You could make a unifying theme if your chosen themes accommodate one another. Consider 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 choose to do an around-the-world theme with your living room; this is sort of a miniature version of Disney's Epcot. You might 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.