How to use xpointer with Xinclude to reference elements

I want to merge 2 XML files with the same structure to make one. For example;

Test1.xml

<?xml version="1.0" encoding="UTF-8"?>

<ns:Root
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ns="urn:TestNamespace"
    xsi:schemaLocation="urn:Test.Namespace Test1.xsd"
    >
    <ns:element1 id="001">
       <ns:element2 id="001.1" order="1">
           <ns:element3 id="001.1.1" />
       </ns:element2>
       <ns:element2 id="001.2" order="2">
           <ns:element3 id="001.1.2" />
       </ns:element2>
    </ns:element1>
</ns:Root>

and Test2.xml

<?xml version="1.0" encoding="UTF-8"?>

<ns:Root
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ns="urn:TestNamespace"
    xsi:schemaLocation="urn:Test.Namespace Test1.xsd"
    >
    <ns:element1 id="999">
        <ns:element2 id="999.1" order="1">
            <ns:element3 id="999.1.1" />
        </ns:element2>
    </ns:element1>
</ns:Root>

To create

TestOutput.xml

<?xml version="1.0" encoding="UTF-8"?>

<ns:Root
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ns="urn:TestNamespace"
    xsi:schemaLocation="urn:Test.Namespace Test1.xsd"
    >
    <ns:element1 id="001">
       <ns:element2 id="001.1" order="1">
           <ns:element3 id="001.1.1" />
       </ns:element2>
       <ns:element2 id="001.2" order="2">
           <ns:element3 id="001.1.2" />
       </ns:element2>
    </ns:element1>
    <ns:element1 id="999">
        <ns:element2 id="999.1" order="1">
            <ns:element3 id="999.1.1" />
        </ns:element2>
    </ns:element1>
</ns:Root>

ie one XML file with all the elements from e