User metabox display First & Last name

Hi guys,

Hope you're well.

Just after a little advice; I have over 1000 users and they only have their firstname as the their display name so I'd like to display their first & last name - when I try the filter below they return blank; any ideas on this one?

Thank you

function wtw_user_filter($label, $field, $user) {
    return $user->first_name;
}
add_filter('rwmb_wtw-user_choice_label', 'wtw_user_filter', 10, 3);

function contacts_user_restriction($meta_boxes) {
    $prefix = 'wtw-';

    $meta_boxes[] = array(
        'id' => 'user-restriction',
        'title' => esc_html__( 'Restrict content by user', 'wtw' ),
        'post_types' => array('contacts'),
        'context' => 'after_editor',
        'priority' => 'low',
        'autosave' => 'true',
        'fields' => array(
            array(
                'id'   => $prefix . 'user',
                'field_type'  => 'checkbox-list',
                'type' => 'user',
                'name' => esc_html__( 'Users', 'wtw' ),
                'desc' => esc_html__( 'Select users who can view this contact.', 'wtw' ),
            ),
        ),
    );

    return $meta_boxes;
}
add_filter('rwmb_meta_boxes', 'contacts_user_restriction');