Regarding Barcelona, this is one of the easiest cities in Europe to do on your own. All you need is to buy yourselves a decent guide book and just have fun. English is widely spoken and you will find that menus in almost every restaurant and cafe are available in English (and several other languages). The main tourist area of the Ramblas and adjacent Gothic Quarter is best explored on foot. The Gaudi designed Cathedral (Sagrada Familia) can be accessed by the efficient Metro system, a taxi, or a 30 min walk from the Ramblas. Regarding your other ports, there are always options other than the overpriced cruise line tours. You can do your pre-trip homework and do most any port on your own (Venice and Dubrovnik are easy) or you might want to consider doing a private tour (you can find a lot of info on the internet). You have lots of time to do your research and after more than 40 years of extensive international travel we have found that the homework phase can be lots of fun and help build excitement for your trip. We have spent many a day in a large Borders book store sipping cappucino and reading through travel books.