This can be done by licencing all those works for free, there are many recources out there that are royalty-free. If someone explicitly states his work can be used by others or Larian, Larian can use it.
All you basicly need to do is group all works and artists under a royalty-free "label", all artists are volunteers and are credited.
I don't think copyright can be a problem if you intent for larian to use (written statement).
