Let me attempt to answer all the questions together the best I can.
What does metaphysics mean - it means a meaning deeper than what meets the eye. Did Draupadi's five husbands exist, mother in law exist, so and so existed and so on are questions that cannot be answered. In simple words - nobody knows whether or not they did. So we can look at it in two ways - we can examine the Mahabharat like history to prove or disprove whether or not they existed.One. Or we can let ourselves believe that the story was an ALLEGORY to deeper spiritual truths - that does not mean they did not exist, it means what the story signifies is MORE important than literal examination of their existence.
Third point - the deeper meanings of the Mahabharat are mind blowing and made it hard to beleive it was a literal story or happening - in other words RRJ had fifteen wives, Akbar and Krishnadevaraya had a harem - these things do not mean anything beyond historical facts. But why did Draupadi or Kunti have FIVE husbands (ok kunti had an additional one for other reasons but still). It corresponds to something on a metaphysical realm. It is not just this one fact but every person and every act in the Mahabharat is known to correlate to karma and Patanjali's Yoga Sutra. This has been examined in great detail by Adi Shankara and later on by Paramahamsa Yogananda.
Lastly - if you want to enjoy the Mahabarat as a 'cut and dry' story as someone put it - by all means go ahead. There is nothing wrong and it takes a lot of effort and difficulty to understand the deeper meanings, not everyone has to. My only appeal is not to reduce it to a story and a literal social happening of some period of time. It is not. One can use an elephant to mow the land or a drive a race car to work but that is not what they are meant to be. Even if we do not understand we have to respect the deeper spiritual truths behind the story - next time someone comes up with a dumb question on Draupadi being married to five men or Jayadratha killed by deceit or any other character just say it is possible to explain on non literal terms. But if you engage in an 'ettikku potti' kadhai like those patti mandrams that argue on a literal basis then dont blame them for counter arguments and it is not possible to justify the Mahabharat this way that is all.