Who were the characters of the story The Twenty-One Balloons?who was in this story

The main character of this story is a teacher named Professor William Sherman who takes a balloon trip and lands on a Pacific island called Krakatoa.  The island is home to 20 families who share the wealth of a diamond mine and must keep their treasure a secret.

The 20 families, who live on the island have alphabet names, Family A, etc. The Professor is the only real character in the book.