1) Why Princess Celestia is not a Queen? Who are the Queen and King!?
In ancient Rome, the people deposed a tyrannical king; since then, "king" was all but a dirty word. Even after the emperors' rule became increasingly autocratic, they (at least formally) kept the republican institutions. I've had a theory that the reason why Celestia was a princess rather than a queen was similar: perhaps at some point the ponies deposed an evil king (perhaps king Sombra himself), and since then, Equestria did not have a king. (Of course, since then the 'Journal of the Two Sisters' came out, which complicates the things.)
8) How was Equestria made!?
"And Princess Lauren said: Let there be ponies. And there were ponies." On the other hoof, perhaps it was Princess Bonnie who created the ponies, while Princess Lauren was the creator of Equestria.
9) Celestia and Luna's parents!?
Princess Lauren and Prince Craig?