How to propely add views grouped filters with exposed filter in one of them
I am still waiting for a response to do this more elegantly but since I am in a hurry I wrote a query alter to accomplish what I need. Maybe it's helpful to someone

function custom_views_query_alter(&amp;$view, &amp;$query) {
  if ($view-&gt;name == 'ts_group_events' &amp;&amp; $view-&gt;current_display == 'calendar') {
    if (empty($query-&gt;where[2]['conditions'])) {
      foreach ($query-&gt;where[1]['conditions'] as &amp;$condition) {
        if ($condition['field'] == 'node.type' &amp;&amp; $key = array_search('birthday_event', $condition['value'])) {
          unset($condition['value'][$key]);
        }
      }
      $query-&gt;where[2]['conditions'][] = array(
        'field' =&gt; 'node.status',
        'value' =&gt; 1,
        'operator' =&gt; '='
      );

      $query-&gt;where[2]['conditions'][] = array(
        'field' =&gt; 'node.type',
        'value' =&gt; array('birthday_event'),
        'operator' =&gt; 'in'
      );

      $query-&gt;where[2]['conditions'][] = array(
        'field' =&gt; 'og_membership.gid',
        'value' =&gt; NULL,
        'operator' =&gt; 'IS NULL'
      );
    }
  }
}