Is it possible to replace more than one form element (wrappers) triggered by only one #ajax trigger element?
Instead of returning the HTML of the single element to update, your ajax callback can return an array of ajax commands. So it can return two ajax_command_replace to replace each element.

function ajax_example_simplest_callback(&amp;$form, $form_state) {
  return array(
    '#type' =&gt; 'ajax',
    '#commands' =&gt; array(
      ajax_command_replace("#replace_div_1", render($form['element_to_be_replaced_1'])),
      ajax_command_replace("#replace_div_2", render($form['element_to_be_replaced_2']))
    )
  );
}