Poseidon never died in Greek Mythology, being a god both immortal and ageless he can not die.
If you believe in Greek mythology, yeah.
Poseidon is a figure from Greek mythology, so you can learn more about him by reading ancient Greek texts like the Iliad and the Odyssey. You can also find information about Poseidon in books about Greek mythology, or by exploring websites dedicated to Greek gods and goddesses.
Um...the Greek god...No he doesn't, and he never did. Though it would be cool if he did. He was one of the supernatural beings that the ancient Greeks came up with to explain the movements of the weather and other unexplainable happenings.
In Greek mythology when Athena is the daughter of Zeus, Poseidon being the brother of Zeus, is her uncle. However, myths exist which make Poseidon the grandfather of Athena when she is the daughter of his son Triton, or Poseidon is the father of Athena when her mother is Tritonis or Polyphe.
Minotaurs do not exist, it was a creature from Greek mythology
In Greek Mythology, yes.
No, it is a creature in Greek mythology
Vampires don't exist... they are Mythology.
No.
Janus did not exist in ancient greek mythology.
Greek Mythology pre-dates Noah and the tales of the Bible; so, yes, it did, so too did Egyptian Mythology.
Poseidon