[Jellby]

Separate HTML files = separate pages.

There's nothing you can do in the book about it. At most, there might be a reader option to show a double page layout, but that's outside Sigil's scope.

Now, if you put both images in the same HTML file, it could be something like:

img {display:inline;max-width:50%;max-height:600px;}

<div><img alt="" class="height" src="../Images/china1.jpg" /><img alt="" class="height" src="../Images/china2.jpg" /></div>