1. Do we need passports?
2. Tipping on the vessels, how much?
3. Just two adults, is there any suggestions on anything cool for the cruise (granted we are both kids at heart!)
Are we SURE we don't "need" passports? I think technically we do.
Castaway Cay is not part of the U.S. but is technically in the Bahamas, a foreign country. We needed passports for our two-night cruise to nowhere this past weekend because the Disney Wonder sailed into international waters.
If you don't have/bring your passports, you're risking being denied boarding. I would NOT risk that.
Also, even if Disney doesn't require passports, say you experience a medical emergency while on Castaway Cay; in order for them to fly you to a hospital in the Bahamas, you would need your passport.
You still have plenty of time to get new passports, but I wouldn't put it off if I were you, especially if you have to gather up your paperwork (certified birth certificate, etc.), as those can take time depending on where you're obtaining them from.
As for things to do, there's SO MUCH to do! The most important thing you want to do is to pore over the Personal Navigator. It looks like a newsletter and you get one for every day that you're on board the ship, and it will give you a schedule of what's happening that day.
As first-timers it might be hard to get a reservation, but you might see if you can get reservations for Palo (either dinner or the brunch buffet) or Remy. The latter is themed after the famous rat in "Ratatouille" but with very subtle high-end decor. If you have never experienced a high-end classical French restaurant, it's a slightly modern version of Victoria & Albert's at Grand Floridian (but you won't get a personalized menu, etc.). and both of those venues will allow you to experience a very fancy meal without shelling out $200 per person.
Since you don't have kidlets, you might consider a late seating for dinner. Fewer kids that way, and you have more time during the day to do stuff.
There are evening shows in the theater, movies shown all day in the movie theater, a wonderful spa (get a couples massage--again, must book very early), great fitness center, jogging deck, adults-only pool and area, and all the food you could ever want.
Don't know if you've cruised on other lines... about the only thing you do not get on a
Disney cruise ship is gambling and adult cabaret shows. They still have adults-only stand-up comedy and stuff but no cabaret shows. Instead, you get wonderful Disney-quality musicals and things that are wonderful.
... and then, you can always lounge by the pool and sip mai tais all day, too!