add_filter('publish_people', 'people_postdata', 100);
function people_postdata($post_id) {
    global $wpdb;
    $firstname = get_post_meta($post_id, 'first_name', true);
    $lastname = get_post_meta($post_id, 'last_name', true);
    $email = get_post_meta($post_id, 'email_address', true);
    $password = get_post_meta($post_id, 'password', true);
    $username = preg_replace('/[^A-Za-z0-9]/', '', strtolower(get_the_title($post_id)));
    $userargs = array(
        'first_name' => $firstname,
        'last_name' => $lastname,
        'user_login' => $username,
        'user_email' => $email,
        'user_pass' => $password,
        'role' => 'basic'
    );
    // var_dump($userargs);
    wp_insert_user($userargs);
}

add_action('acf/save_post', 'people_postdata', 20);
function people_postdata($post_id) {
    global $wpdb;
    $firstname = get_post_meta($post_id, 'first_name', true);
    $lastname = get_post_meta($post_id, 'last_name', true);
    $email = get_post_meta($post_id, 'email_address', true);
    $password = get_post_meta($post_id, 'password', true);
    $username = preg_replace('/[^A-Za-z0-9]/', '', strtolower(get_the_title($post_id)));
    $userargs = array(
        'first_name' => $firstname,
        'last_name' => $lastname,
        'user_login' => $username,
        'user_email' => $email,
        'user_pass' => $password,
        'role' => 'basic'
    );
    // var_dump($userargs);
    wp_insert_user($userargs);
}