Complex sentence: The Greys lost hope of marrying her to Edward VI and contemplated marrying her to Edward Seymour, 1st Earl of Hertford, son of the Lord Protector and Anne Stanhope.
Split into simpler sentences: The Greys lost all hope of marrying her to Edward VI. They contemplated marrying her instead to Edward Seymour, 1st Earl of Hertford, son of the Lord Protector and Anne Stanhope.