I've got two weeks in August with wife and two daughters, 15 and 11.

Thought Tuscany might be the trick for one of those weeks and maybe the Amalfi Coast for the second, though I'm a little concerned about costs.

In Tuscany, I thought a villa stay would be the best experience. Should I seek a villa with the resident family on location?

While I'd like them to see wonderful sites like Venice and Pisa, I also thought their best experiences would be exposure to the lifestyle and pace outside of the cities.

Any best thoughts from seasoned travelers about a balanced itinerary, not too fast-paced and full of the reality and sensibility of the Italian lifestyle?

Designer, repost with the area in your title otherwise many will not answer.

Since you are "a little concerned about costs," try an agriturismo or a villa with a pool (for the girls) for one week. Then I will deviate from your planned itinerary by suggesting a week somewhere on Lake Garda. The Amalfi peninsula usually becomes a madhouse of people and traffic in August. The kids would probably enjoy Pisa, but I wouldn't spend more than a half day trip from wherever you are staying. As for Venice, you be the judge. It will be hot and crowded. If the trip is in large measure for the kids, you need to decide if they would like Venice.

I have no idea where you will be arriving in Italy, which will also influence your overall plan. Arriving in Rome versus Milan versus Venice might make your itinerary look quite different. Maybe you could tell a little more about your overall plan.

Personally I would go further north in August. It will be pretty hot. How about Germany or Scandinavia; or Scotland

I agree that Scandinavia would be a good choice; in the UK and Europe, August is the BIG vacation month. Things will be crowded, and already many lodgings will be booked and you might not have much from which to choose. Otherwise I would heartily recommend Scotland and Germany as well, although Germany in August can be quite hot and humid. But then so might Italy.