the end of the game how does Kuja (SPOILER) cause an earthquake and cause mist to be produced again through all those roots, when that Soulcage monster is dead? And why does the Iifa tree have a violent reaction after the final battle? Also are we to assume that mist still completely covers Gaia and that's why Vivi has kids?

If any of you know the answers to any of these questions that would be great.