How to control flow across blocks
I couldn't find any controls that would allow me to stop this floating across blocks behavior. I was under the impression that each block in a stack was starting a new line on the page, so I am confused about this behavior. Sorry for such a basic question.
The Content block is not best suited for creating images in a row like that.
An alternative is to make a custom layout with four columns to hold the images. Add a Content block above and below it with your text.
If you need more control, you can add a custom layout preset.
Please see attached screenshots.
It looks like you are using clear both as an approach for this issue.