Main Menu and Sub Menu Items for Footer

This is actually not that difficult if you already know how the walker class works. You would need two calls to wp_nav_menu. The first one you have should already work, because the function natively allows you to select only the top level.

What it doesn’t allow you to is to select everything but the top level. So you need a separate walker, which you would call like this:

wp_nav_menu( array(
    'theme_location' => 'primary',
    'walker' => new wpse215647_walker(),
    'container' => false,
) );

In your walker you must make sure all items are included, except the top level. That question already has an answer here.