More columns in the portfolio or in the blog overview

you can increase the Column Count number there at the drop-down by making appropriate changes in the portfolio.php.

you can download the whole portfolio.php from pastebin:
( this is on basis of enfold 4.8.7.1)
look: https://pastebin.com/v1s9sdQb
download: https://pastebin.com/dl/v1s9sdQb

This new portfolio.php you can upload via ftp to a folder named shortcodes in your child-theme folder:
child-theme/shortcodes
To load those edited child-theme alb elements ( see docu ) – you had to place that snippet in your child-theme functions.php:

function avia_include_shortcode_template($paths){
  $template_url = get_stylesheet_directory();
      array_unshift($paths, $template_url.'/shortcodes/');
  return $paths;
}
add_filter('avia_load_shortcodes', 'avia_include_shortcode_template', 15, 1);

after that in the dom the portfolio will have that extra class : grid-col-8 ( in your case )
now you only have to put this to your quick css ( or something similar ):

.grid-col-8 .grid-entry {
  width: calc(12.5% - 8.75px) !important;
  padding: 0;
  margin: 0 10px 10px 0 !important;
}

.grid-col-8 .grid-entry:nth-child(8n) {
  margin-right: 0 !important;
}

ps: 8.75px because 8cols will have 7 spaces between with a setting of 10px it is 70px total space 70px/8 = 8.75px