Should be easy enough. First, get the City.
<?php $city = get_field('city'); ?>
Then in your WP_Query, insert the taxonomy parameter:
<?php $loop = new WP_Query( array( 'post_type' => 'member', 'posts_per_page' => -1, 'location' => $city ) ); ?>
Et Vilola: you only get the Members that have the taxonomy $city.