merge jQuery, own-child.js and avia-footer-scripts into one

Hi,
currently jQuerry, my own JavaScript (main-child.js) and avia-footer-scripts… .js are called by seperate HTTP-requests.
(at least, that is what I see in my Chrome network tab)

Here is how I load my custom JS from my childs functions.php

function custom_scripts(){
    ?>
    <script type='text/javascript' src="./wp-content/themes/enfold-child-fecgz/js/main-child.min.js" defer='defer'></script>
    <?php
    }
    add_action('wp_footer', 'custom_scripts');

My two questions are:
1. Is it possible to combine all three js files into one?
I could just paste the jQuery code into my custom,js for example.
Then it just needs to be merged with the other js fie from the theme.

2 Is jQuery really needed for the theme or can it be removed if I will do without some functions of the theme?