You could make 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 as part of your living room; this is sort of a miniature version of Disney's Epcot. You may incorporate Asian tropic plants, samurai and dragons swords that would incorporate all three themes. The idea is, regardless of the themes, there is common ground to be found.