Can SOAP body have multiple immediate children without splitting the msg

Question

We have a vendor we need to send a SOAP message to, but they require the SOAP body have two different immediate children.  In graphical mapping this doesn't seem to be possible. 
If we create separate external definitions for each, then they would become separate target messages once added to a message mapping.  If we try to combine the XSDs into one, import it as an external definition, and add it to the mapping, It prompts us to choose one of the elements of the external def from the top level.  The only way to choose a second is to add another, which again results it two separate target messages.
Is our vendor's request compliant with W3C standards?  If so, is this just a limitation of graphical mapping and what are the most common workarounds in PI?

Answer 1

>>If we create the SOAP envelope with our mapping, then does that affect the ability to use the SOAP adapter to provide a digital signature?
This is what I would do. Consider synchronous scenario. If you sign the message digitally and send it to system A (say outbound)  and you need to have the same soap message structure (inbound)  during signature verification. Otherwise signature verification process will fail.
Do as follow
Outbound
A) First mapping: Adding soap envelope  using (XSLT mapping) or java mapping or any way
B) Second mapping: Signing the message using digital signature via java mapping
Inbound
First mapping should be digital signature verify using java mapping
if the requirement to remove/modify saop envelope on the inbound side or any changes in structure only after the signature verification