You can create 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 plan to do an around-the-world theme with your living room; this is like a miniature version of Disney's Epcot. You might incorporate Asian tropic samurai, dragons and plants swords that would incorporate all three themes. The thing is, regardless of the themes, there may be common ground available.