Hi. Congratulations on your upcoming journey aboard with the Disney Cruise Line!
Since Mickey gives me limited space to answer questions, I'm going to provide a couple of links to insure that you get all of the info that you need.
First, check
here about formal nights. You'll find that a shirt and tie is just fine for your husband and I especially recommend packing lighter given all of the new airline fees for checked luggage.
Your daughters will find some wonderful activities. Check
here for more information. There will be single mingles, dancing, quiet time at the adult pool, planned activities at the adult pool and other events tailored for young adults. They can surf the internet (for a fee), hang out in the Cove Cafe (coffee bar), take a fitness class, visit the spa, take a nap, relax at sea, play bingo, shop, attend movies and shows and plan their shore excursions in the next Port-of-Call.
Disney really does cater to all ages!