You can target these images with CSS, either float or inline block. The problem you face is how to discriminate between images you want to have inline and those you don’t.
You could add a tag to the post, eg gallery and then target that, but I think you’d need jQuery to select the target for the style as the tag element is a sibling of the topic body, not a parent (from memory in any case).
You could also encode something in the img alt tag and target that. That works fine with CSS but it’s a bit messy.
Alternatively, I use a gallery plugin from Flickety in my test site:
It’s overkill for what you say you need, but does give good results. This carousel picks up on the carousel tag and renders a carousel - it also works with lightbox. I will post code at some stage, but not until I’ve managed to find out how to load the gallery script with require…
