We've ridden our tandem in several European countries, including Italy. Tandems may not be as maneuverable as single bikes, but are still way better than the cars that use the same roads, so we've never had a problem in that respect, and I wouldn't worry about it.

Italian drivers do some mad things, but they seem to treat cyclists quite reasonably, so I also wouldn't worry about that too much. In fact, I would fear drivers in most European countries less than those in North America because the North Americans fall asleep at the wheel far more often due to their roads typically being straight, long, boring, distances between towns being further, and driving distances in general being so much greater than in Europe. I'll always take a narrower, more twisty European road with a village every few kms, and so with mostly alert drivers on it over a wide but straight North American road full of drivers only half paying attention.

Finding a place to rent a tandem in that area may be the biggest challenge, and unfortunately I don't have any tips for that region.