Hello @Tony_Casey,
Bullet Point #1 is discussed here by Mike: No artist listed for unidentified comps, you can give that thread a read but essentially it says that the right data for Track Performer is not listed, then it could show up as Various Artists.
Bullet Point #2 artist equivalency issues are discussed in this thread: (Artist Equivalence Issues). I would double check the Album Browser/Track Editor to make sure that the composer is not listed twice in the file data, and you can always edit the credits in track editor to prefer your edits rather than the Roon metadata.
As for bullet point #3, I am not too familiar with joint compositions, tagging @joel here in case he wants to take a look at what could be going on and can possibly recommend a way to search joint compositions.
Hope that helps.
Thanks,
Noris