If is multiple page templates

I you want the script be enqueued on page-index.php and page-contact-us.php, then you must check that that page templates are used but you are checking if they are not used.

Chagne this:

if ( !is_page_template('page-templates/page-index.php') && !is_page_template('page-templates/page-contact-us.php') ) {

with:

if ( is_page_template('page-templates/page-index.php') || is_page_template('page-templates/page-contact-us.php') ) {

The first code reads like: if is NOT page-templates/page-index.php AND it is NOT page-templates/page-contact-us.php …

The second conditional reads like: if IS page-templates/page-index.php OR it IS page-templates/page-contact-us.php ….

You can use also an array of page templates to be checked:

if ( is_page_template( array( 'page-templates/page-index.php', 'page-templates/page-contact-us.php') ) ) {