Norman,
The Name will always be populated. Either you specify the name OR you specify the Given and Family name and it populates the Name field with those values.
Try this example. Login to QuickBooks online, enter the first, middle and last, then the display name populates automatically.
Here is the XML example when I only enter First Name, Last Name
<Name>Jazz, Hugo</Name>
<WebSite/>
<Email/>
<GivenName>Hugo</GivenName>
<MiddleName>J</MiddleName>
<FamilyName>Jazz</FamilyName>
regards,
Jarred