You can enqueue all your scripts the same way as you enqueue jQuery.
Register and enqueue all your Javascripts like this (in your load_jquery function)
wp_register_script (
'yourscripthandle', //string $handle: a string to identify this script
get_bloginfo( 'template_url' ) . '/js/yourcustomjs.js', //string $src: Path of your script file
array ('jquery' ), // array $deps = array(): defining which scripts your script is dependend on. In your case, it's jQuery.
'', // string|bool $ver = false: The version of your Script
true //bool $in_footer = false: whether your script should be enqueued in `wp_head()` or `wp_footer()`
);
wp_enqueue_script( 'yourscripthandle' );
Afterwards you just need to make sure that you set $in_footer to false, if you need the scripts in the header.
Also make sure your theme calls wp_head()!
The problem with loading jQuery two times seems to be that it is included after your scripts are called – so adding it a second time befor the others solved that issue. Please be sure to correct this, as this is going to have implications on a lot of stuff.