Supernatural established that John never knew Mary was a hunter and he didn't become one until after Mary's death. Even when they got attacked by the angel Anna (after they were married) and he did find out about Mary being a hunter, those memories were erased by Michael.
(X) It is revealed by Dean in #1.13 (the series finale) that The Winchesters is set on an alternate Earth, so what happened on Supernatural may not have necessarily happened here.
(X) It is revealed by Dean in #1.13 (the series finale) that The Winchesters is set on an alternate Earth, so what happened on Supernatural may not have necessarily happened here.