I have edited your question to deal exclusively with "An Occurrence at Owl Creek Bridge," in accordance with eNotes policy of answering only one question per posting.
Ambrose Bierce's story deals with a minor incident that occurs during the Civil War. Peyton Farquhar must be considered the protagonist, since he is the only major character in the story. He makes the decision to try to destroy the Owl Creek Bridge and finds that he has walked into a trap. The reader is locked inside Farquhar's consciousness from the very beginning, when he is standing on the bridge with a noose around his neck, to the very end, when the slack runs out and the rope breaks his neck. The real time involved is only seconds, but it seems like many hours to the protagonist.
The antagonist is not identified, but the reader can assume that the senior officer in command of the detechment of Union troops guarding the bridge was the one who set the trap to catch any Southern sympathizer and is therefore the antagonist.