Hi Leigh!
First, let me confess just how jealous I am! The Disney Cruise from Barcelona through the Mediterranean might just be the cruise of my dreams! I hope it meets and exceeds all your dreams as well!
Now, on to your question! During the day, you'll feel comfortable at just about every dining venue in your most casual clothes. Bathing suits will not be allowed in the main dining areas, so if you're interested in just a quick meal without having to change from your pool attire, then a meal at Goofy's Galley, located right on Deck 9, is a great choice.
Dinner, however, is a bit different. Each night the suggested attire will be listed in your Navigator (your daily planner/listing of activities). Most cruises feature cruise casual nights, a semi-formal night and at least one formal night. For cruise casual, the men in our family usually opt for khaki pants and a collar shirt. For semi-formal night, they will add a jacket. As for formal night - its up to you! You can opt for a suit and tie or for a tuxedo. You'll see an incredible mix of attire on formal night and it really increases the magic to be a part of the glamor! Your wife and daughter will be perfect in slacks, skirts or dresses on cruise casual night and in very nice pants or dresses on the other nights. Be sure to have them bring a light wrap as well - I always seem to be chilly in the dining rooms!
Disney Mom Andi had some great suggestions about formal night in one of here
answers. Be sure to check that out as well!
Hope this helps!