I hate to sound like a brown noser but I'm going to anyway.  Renderosity have, for reasons best known to themselves, tightened up on the issue of Read Me's and how they must be worded and if they are not worded exactly as shown on their Submission Guidelines it is an immediate fail.  The tester is only doing what they have been instructed to do in the way they have been instructed to do it.  Part of that is that the merchant name in the Read Me has to match the merchant name of the vendor account so, it she is right to ask you to put VanishingPoint as opposed to the individual names. 

Maybe write back and copy in one or both of the store admins and ask if:

"All of this products content was created by jhoagland and mrsparky collectively known as VanishingPoint"

 would be acceptable.  To me that would fulfil all criteria as specified by their guidelines but as I am neither an admin or a tester I can only guess.