You can create a unifying theme if your chosen themes accommodate one another. Think of 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 opt 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 incorporate Asian tropic samurai, plants and dragons swords that would incorporate all three themes. The thing is, regardless of the themes, there is common ground found.