How appropriate is to make multiple submissions of research findings to same venue/conference?
You cannot submit both papers.  As others have pointed out, most venues explicitly forbid simultaneous submission of substantially overlapping papers.  The answer to your first three questions is the same: Immediate rejection.

In fact, I would go further: Neither PA nor PB can be submitted alone.  It is unethical to submit a paper without the explicit consent of all authors, because authorship implies endorsement of and responsibility for the content of the paper.  On the other hand, it is unethical to revoke authorship from someone who has made a substantial intellectual contribution to the work.  The two authors must work out their editorial differences, like grown-up professional adults, before they can submit anything.

If they can't agree on what to submit, then tough noogies — no paper.