That creature was a part of Voldemort's soul sent there to die.
Dumbledore.
Yes, when Harry is in 'limbo' he meets Dumbledore and they talk.
Dumbledore never told Harry about the Deathly Hallows because he was afraid that Harry might try to chase after them. Now, Dumbledore knows he is much more of a man.
The chapter is 'The Will Of Albus Dumbledore'.
Kendra and Arianna Dumbledore?
It's about Harry Potter and the Deathly Hollows. And about Voldemort, Dumbledore, Horcruxes and many other things.
No.
yes. the stone is in the snitch and dumbledore has the elder wand
Yes. After Voldemort tries to kill Harry in the Forbidden Forest, Harry enters a dream-like state where he talks to Dumbledore.
Harry, Ron, Hermione, Voldemort, Severus Snape and Albus Dumbledore,
Yes. He died in Harry Potter and the Half-Blood Prince.
Chapter 12.