Who is the protagonist, antagonist, and catalyst? What is the theme? What is the conflict?none

Laurie/Charles appears to be the answer to each of your questions.  Laurie is the protagonist (the well-rounded main character) and Charles is the antagonist (causing trouble wherever he goes.  The catch, of course, is that one person is both, though we don't realize it until the end.  Both are actually fairly round, dynamic characters who do nearly all the actions--both good and bad--in Shirley Jackson's "Charles."  If that's the case, you can probably assume this character is the cause of everything else in the story.