How many people do you have to meet to help Thomas Edison on mystery train island?

You have to talk to all of the people on the mystery train, from the coalman in the front (right) to the guard in the back (far left). There are the 4 crew (conductor, coalman, porter, guard) and 8 passengers besides Edison (New York Times Reporter, Mlle. Moreau from Le Monde, Gustave Eiffel, George Ferris, Nikola Tesla, Eric Weisz, Mark Twain, and Susan B. Anthony).