Jane Fairfax was actually going to Hogwarts when she moved out of Highbury as a child.
She left before she was 9, the reason being that she was going to be taken care of by the Campbells after her parents died. That's just the right time for her to go to Hogwarts, which would have been in operation for a few centuries at that time. It would have been about 3 years after her graduation by the time she returned more permanently at the age of 21 during the novel.
The Campbells probably have one magical person in their family who recognised that Jane was showing signs of magical ability during her visits. By inviting Jane to live with them, Colonel Campbell was not only taking care of his late friend's daughter, he was also ensuring that there would be a magical adult to teach her how to control her magic until it was time for her to go to Hogwarts.
Mr. Knightley, tragically, died young.
Emma married again. Her second husband's name was Norris.