Upload mobi and epub file in the MEDIA of WP

Sounds like you need something like:

add_filter('upload_mimes', function ( $mimes = array() )
{ 
    $mimes['mobi'] = 'application/x-mobipocket-ebook';
    $mimes['epub'] = 'application/epub+zip';
    return $mimes;
} );

to support the uploads, but you might have to adjust the mime types to your needs.