I’m trying to set full width in pages content, but this is set by default to 8 columns (col-md-8 in div class) although there’s no content in sidebards.
I would like this <div class="col-md-12 la-content-inside">
There is already page template for pages. You can select page full width template on a specific page you wish to have full width. Please go through this tutorial, this might help you.
And if you wish to have on post you need to customize single.php templates keeping on child theme.