You can create a unifying theme if your chosen themes accommodate one another. Look at 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 inside your living room; this is sort of a miniature version of Disney's Epcot. You might incorporate Asian tropic dragons, plants and samurai swords that would incorporate all three themes. The point is, regardless of the themes, there is common ground can be found.