Same or different instances of a JavaScript code?

This is the bottom of my webpages. As you can see, there are several instances of jquery.min.js.

    <!-- JavaScript at the bottom for fast page loading -->
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script><!-- Changed from src="/ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" -->
    <script>window.jQuery || document.write('<script src="/mysite/js/jquery-1.7.2.min.js"><\/script>')</script>
<!-- Responsive Grid System -->
    <script src="/mysite/js/responsivegridsystem.js"></script>
<!-- Responsive Menu Acordeón -->
    <script src="/mysite/js/accordionmenu.js"></script>
<!-- For automatic applying of a webp or no-webp class to HTML element, depending on browser support -->
    <script src="/mysite/js/modernizr-custom.js"></script>
    <script>
      Modernizr.on('webp', function (result) {
        if (result) {
          // supported
        } else {
          // not-supported
        }
      });
    </script>
<!-- Carousel -->
    <script src="/mysite/js/jquery.min.js"></script>
    <script src="/mysite/js/slick.min.js"></script>
    <script>
    $('.carousel-view').slick({
      dots: false,
      infinite: false,
      speed: 300,
      slidesToShow: 3,
      slidesToScroll: 3,
      responsive: [
        {
          breakpoint: 600,
          settings: {
            slidesToShow: 2,
            slidesToScroll: 2
          }
        },
        {
          breakpoint: 480,
          settings: {
            slidesToShow: 1,
            slidesToScroll: 1
          }
        }
      ]
    });
    </script>
<!-- modal box to work in IE9 -->
    <script src="/mysite/js/jquery.hoverTransition.js"></script>
    <script> amenu.open("88", true); </script>
    <!--[if (lt IE 9) & (!IEMobile)]>
    <script src="/mysite/js/selectivizr-min.js"></script>
    <![endif]-->
<!-- Pretty float pictures-->
    <script src="/mysite/js/prettyfloat.js"></script>
<!-- Make all divs in a row the same height (Responsive Grid System) -->
    <script src="/mysite/js/jquery.matchHeight-min.js"></script>
    <script>
    jQuery(function($){
        $('.matchheight').matchHeight();
    });
    </script>
<!-- Table (tabla) -->
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
    <script>
     $(function() {
            /* For zebra striping */
            $("table tr:nth-child(odd)").addClass("odd-row");
            /* For cell text alignment */
            $("table td:first-child, table th:first-child").addClass("first");
            /* For removing the last border */
            $("table td:last-child, table th:last-child").addClass("last");
    });
    </script>
<!-- Usado para colapsos -->
    <script>
        function toggleDiv(divid){
        if(document.getElementById(divid).style.display == 'none'){
        document.getElementById(divid).style.display = 'block';
        }else{
        document.getElementById(divid).style.display = 'none';
        }
        }
    </script>
<!-- Menu navigation -->
    <script src="/mysite/js/jquery-1.7.2.min.js"></script>
    <script src="/mysite/js/script.js"></script>
<!-- Tooltips -->
    <script src="/mysite/js/jquery.min.js"></script>
    <script src="/mysite/js/tooltip.js"></script>
<!-- Zendesk Live Chat Script -->
    <script>
    window.$zopim||(function(d,s){var z=$zopim=function(c){z._.push(c)},$=z.s=
    d.createElement(s),e=d.getElementsByTagName(s)[0];z.set=function(o){z.set.
    _.push(o)};z._=[];z.set._=[];$.async=!0;$.setAttribute("charset","utf-8");
    $.src="https://v2.zopim.com/?26AnsOGmySbDiEq6CAIx8dIxyvck1SUC";z.t=+new Date;$.
    type="text/javascript";e.parentNode.insertBefore($,e)})(document,"script");
    </script>   
<!-- TrustedSite Script -->
    <!-- Grab Google CDN's jQuery, with a protocol relative URL; fall back to local if necessary -->
    <script src="https://cdn.ywxi.net/js/1.js" async></script>
</body>

This is because each time I use a JavaScript solution for implementing say, a carousel, a menu, etc., the developer gives you instructions about the .js that will be needed.

As I am a newbie in web design, there are several questions I have regarding this:

1. The source of one instance is https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js. Is that better than having the .js in a folder of the website?

2. Are the 4 or 5 instances of this particular .js the same code, I mean, are all of them the same?

   1.1 If not, can I have all of them in a js folder renaming each one differently and then pointing the webpage to them?

   1.2 How the browser/site/software knows which version to call?

   2 If yes, should I take all but one out and everything will work OK? I made a small experiment and took one instance of jquery.min.js out trying to make a carousel work, and even though it still didn't work, at least it behaved better than before.

My googling with different versions of “css3 html5 can a java script file appear several times in the document” brought not an answer.