I am wondering which is the best way to put spaces in between these 3 images with CSS using Bootstrap 3 RC2 as what I have done at the moment is not auto-resizing the images
Remove your own CSS for .col-lg-4: these margins may screw up the Bootstrap CSS. Next to that, these columns are only visible when your screen width is bigger than 1200 px.
Add the following classes to your divs: .col-xs-4 .col-sm-4 and .col-md-4, and give images a class="img-responsive" attribute.
It should work now as you wish.