Sorting by linked node/entity reference fields
Since you haven't been able to see the new fields for ordering (which is odd), you will probably have to perform a query alter on the views query and do some modifications:

&lt;?php
function mymodule_views_query_alter(&amp;$view, &amp;$query) {
  if ($view-&gt;name == 'myviewname') {
    $view-&gt;query-&gt;somecodetoselectfields
    $view-&gt;query-&gt;somecodeforleftjoin
    $view-&gt;query-&gt;orderby[0]['field'] = "FIELDNAME";
    $view-&gt;query-&gt;orderby[0]['direction'] = "ASC";
  }
}
?&gt;


What I usually do is just add a tag on the views query so that I can modify it using the standard Drupal query interface, which is much easier to use IMO.

&lt;?php
function mymodule_views_query_alter(&amp;$view, &amp;$query) {
  if ($view-&gt;name == 'myviewname') {
    $query-&gt;tag[] = 'mytag';
  }
}
?&gt;


Then

&lt;?php
function mymodule_query_mytag_alter(QueryAlterableInterface $query) {
  $query-&gt;blablabla;
}
?&gt;


Take a look at:

https://www.drupal.org/node/310077
https://api.drupal.org/api/views/views.api.php/function/hook_views_query_alter/7
https://api.drupal.org/api/views/plugins%21views_plugin_query_default.inc/class/views_plugin_query_default/7

Apologies if the solution is not straightforward enough.