I did answer it.
"1. Can the JDB do this legally? If not, how can I prove in court that they're doing this?"
You raise the defense that they don't own the debt and have no authority to sue. You seek documents during discovery.
If it's the first question in there that you are concerned with, it should be obvious that it's legal for a plaintiff to file a lawsuit and make allegations even if those allegations turn out to be in error when evidence is presented at trial. That's what the whole lawsuit system is about.

