If they use shortcode, then you would add the shortcode to a text widget for the sidebar column and then the shortcode for the content part in the page editor…or however, you plan to set this up as I’m not sure really how these plugins work and never seen them function. The document gallery one has a shortcode as [dg] which goes in your page. Their installation page has a ton of info, so best half a coffee while you go through it.
I did read that you mentioned about having two content areas…not really or easily possible, but the closest you can get is using inline columns. http://demo.styledthemes.com/celestial-reloaded/content-columns/
