Add Sidebar Footer

You can use the footer column widget areas to place different widgets into the footer of your site.

I’m not sure what you mean by adding a sidebar to the footer? You can see in the apperance > theme options > footer options all the different layout options.

Kadence Themes

You can make the first widget area fullwidth and the next three sit under it. Add this css:

@media (min-width: 768px){
    .footercol1 {width:100%;}
    .footercol2, .footercol3, .footercol4 {width:33.33%}
}

Kadence Themes