Given that this is a very important trip to you and your family, I'd recommend that you take 2 camera bodies, namely the D90 that you currently own and a D610 you would need to purchase. Use the 17-55mm on your D90 and buy a 70-200mm 4.0G to mount on the D610. This should cover almost all of your photographic needs unless you feel you need something giving a wider view in which you could throw in your Tokina 12-24. If this ends up being more than you can or want to invest at this time you might want to look into one of the mirrorless camera options from Panasonic, Sony or Olympus equipped with an appropriate lens as opposed to the D610 and 70-200mm. Hard to buy for another person so what I would go with may not work for you. Have a great trip and post a few photos when you get back.