Multiple story chapters without overwriting
If you’re making a series (a story with multiple chapters), I find that it’s easiest to create a custom neighborhood just for the story. You’ll have your lots to house your character families and different lots for different scenes as you see fit. Then, you can make what I call “dummy lots” to house your chapters to your story.

What is a “dummy lot”? It’s just a blank, small lot with one random Sim living in it. This Sim will have nothing to do with the plot of your story. However, you will use the Family Album for the Sim on this lot to host the pictures you want to include in your story that were taken on other lots in the neighborhood.

What you do is take the pictures from any lot or multiple lots for your story. When you’re ready to make the slides for your story, go back to this “dummy lot”, press the “+” sign in the picture viewer, then select and add your pictures.

Your first chapter was overwritten by your second chapter. What you need to do is upload other chapters from separate families. If you use the same family album, you will erase the upload from that house. You have to rewrite the first chapter again, sadly. Upload the second chapter from somewhere else in the neighborhood.