Board Thread:Naruto Discussions/@comment-28861328-20140618060932/@comment-17623-20140618094259

1) The Ten-Tails is what happens when Kaguya's ego lusts for the worlds chakra and the Shinju tree responds. Turns out, the Shinju itself is not sentient at all. With an eye at the top.

2) Considering Black Zetsu said at least the Sage didn't know that his mother was that crazy, it can be assumed that they didn't know their mother's will caused created the Ten-Tails when they sealed it up.

3) From what I can gather, still the Ten-Tails.

4) Because she is very very selfish and she didn't even want her kids to have it, so damn the world for getting chakra too.