how to notificate users about new created referenced nodes
I think you can accomplish it by creating a custom module. Whenever users create nodes of type B, you can mail and notify those users who created nodes of type A. 

You can get the list of users who created nodes of type A with a SQL query like the following.

SELECT DISTINCT uid FROM node WHERE type = 'goals'


In order to send mails when users create nodes of type B, you will have to implement hook_node_insert(), so that you can send notifications after nodes are successfully created. You could also use hook_node_presave(); the only difference is that the latter will send mails before nodes are created.

function MODULE_NAME_node_insert($node) {
  if ($node-&gt;type == "B") {
    $params = array();
    $from = variable_get('site_mail', 'admin@example.com');
    $send = TRUE;
    $language = language_default();

    // It is assumed that array od users who created node of type "A" is returned
    // by the following function.
    $users = _list_of_user_created_A_node();
    foreach ($users as $key =&gt; $value) {
      $uid = $key;
      $mail = $value;
      $params['node_title'] = $node-&gt;title;// The node title of the created node B
      $params['userID_A'] = $uid;
      $params['mail_of_user_A'] = $mail;
      drupal_mail('MODULE_NAME', 'notify_mail', $mail, $language, $params, $from, $send);
    }
  }
}


See hook_mail() on how sending mails.

You could also save the node titles in a database table, and send mails during cron task's execution.