If the XML have identities with same name in different levels there is a solution. You don´t have to ever submit a raw XML (this PHP SOAP object don´t allows send a RAW XML), so you have to always translate your XML to a array, like the example below:
$originalXML = "
<xml>
<firstClient>
<name>someone</name>
<adress>R. 1001</adress>
</firstClient>
<secondClient>
<name>another one</name>
<adress></adress>
</secondClient>
</xml>"
//Translate the XML above in a array, like PHP SOAP function requires
$myParams = array('firstClient' => array('name' => 'someone',
'adress' => 'R. 1001'),
'secondClient' => array('name' => 'another one',
'adress' => ''));
$webService = new SoapClient($someURL);
$result = $webService->someWebServiceFunction($myParams);
