Complex sentence: These are the arms of his wife's family of Morton, of unknown origin, but said to have been "of Kent" and are the arms borne by John Morton (c.1420--15 September 1500), Archbishop of Canterbury 1486 to 1500.
Split into simpler sentences: These are the arms of his wife's family of Morton. They are the same arms borne by Joan Morton's kinsman, John Morton (c.1420--15 September 1500), Archbishop of Canterbury 1486 to 1500.