Shoutout goes to BlueNerdWriter ! The correct answer was: Jake Lloyd-1
James Earl Jones-4, 5, 6 (most of)
Hayden Christensen-2, 3, 6 (edited in in a new version as a Force ghost near the end)

In the book, Percy Jackson and the Olympians: Sea of Monsters, who replaces Chiron as Camp Half-Blood Activites Director?