Don't have a measurement for ya but I'm 26 and I'm a huge eater, and I have trouble finishing one, although I usually can! My mom, on the other hand, is a light eater and has trouble finishing 2 slices. They are sliced in 6 pieces. I think you can definitely share them, especially if you're going for lunch.
Tiramisu is delicious there for dessert. Also, not sure how old everyone is, but the sangria is delicious, especially after a hot day in the park. Bon appetit!!