Passing theme suggestions to radio and checkbox children
A possible way is to alter the form in which the radio is used if you know its id, or, for a broader solution, check for each form whether the radio is used.
Then you can call this function:

    function MY_CUSOMT_FUNCTION(&amp;$form, $theme_suggestion) {
     foreach (Element::children($form) as $child) {
     if (!isset($form[$child]['#theme_suggestion'])) {
       $form[$child]['#theme_suggestion'] = $theme_suggestion;
     }
     MY_CUSOMT_FUNCTION(&amp;$form, $theme_suggestion)
    }
   }


You can fine tune it to include only the children of your radio though