To get images in a row you will need to edit the HTML to remove the <div></div> tags inserted by Google Sites to align the images - follow these instructions:
This will put your images in a row. If you want them centred then select the images and use the centre text tool.
Google Sites - Images in a row (side-by-side)posted 9 Aug 2008, 18:21 by Stephen Hind [ updated 6 Jun 2014, 08:29 by Unknown user ]
Many people struggle to get images side-by-side in a Google Site: these instructions provide one way to achieve well aligned images.