Complex sentence: When Henry died the castle became the property of his son, Edward VI of England, who gave it to his uncle, Thomas Seymour who was made Thomas Seymour, 1st Baron Seymour of Sudeley and married the King's step-mother, Catherine Parr.
Split into simpler sentences: When Henry died the castle became the property of his son, Edward VI of England, who gave it to his uncle, Thomas Seymour. Thomas was made Lord of Sudeley and married the King's step-mother, Catherine Parr.