You don't need to include 2 tablesorter library. You need just one. You could include just the "jquery.tablesorter.min.js".
Look the difference between "file.js" and "file.min.js": What's the difference between jquery.js and jquery.min.js?
And you also need to include jquery library.
Example:
<head>
<title>Test Header</title>
// Here you need to include jquery library
<script src="~/Scripts/jquery.tablesorter.min.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$("#tab").tablesorter();
});
</script>
</head>