A witty yarn. 'Witty' indicates cleverness and humor, and 'yarn' is another word for a story. So a witty yarn is a great alternative.
A jocular anecdote. 'Jocular' means given to joking or jesting. An anecdote is a short and interesting story, and when it is jocular, it is surely a funny story.
A farcical story. Farcical means something extremely funny in a rather absurd way.
Yes, 'antecedents' can also be a word for back story. Antecedents are things that have happened or existed before a particular event or situation. When we talk about a character's antecedents, we are referring to their past experiences, family upbringing, and any events that have influenced who they are in the present, which is all part of their back story.
Sketch. This word can be used to refer to a short story as it gives the idea of a brief and often rough or unpolished piece of writing, similar to a quick sketch in art.
Central figure. Just like in 'Romeo and Juliet', Romeo and Juliet are the central figures. They are the ones the story is mainly about, and their relationship and the events around it form the core of the play.
Family chronicle. It's like a record or account of family events over time.
Yarn. This is a more informal way of referring to a story, often used when the story is a bit of a tall tale or something that might be exaggerated for entertainment purposes.
Narrative. It is a general term for a story, and when it's long and continuous, it can be used to describe what you're looking for.
'Spinning a yarn' is also a way to say telling a story. It has a more informal and perhaps even a bit of a creative or fanciful connotation. Sailors used to spin yarns (tell stories) about their adventures at sea, often with a touch of exaggeration to make the story more exciting.
Superb anecdotes. An anecdote is a short and interesting story about a real incident or person. 'Superb' emphasizes the high quality of these short stories, making it a valid alternative for 'good stories'.
Fan - written story. Since most fan fiction is written by fans, this term makes sense.