Complex sentence: Edmund Dudley's son, John Dudley was the Duke of Northumberland and now having a severe disliking for Royalty, he also plotted to overthrow the king by getting his son (Lord Guilford Dudley) to marry Lady Jane Grey.
Split into simpler sentences: Edmund Dudley's son, John Dudley was the Duke of Northumberland. He also plotted to overthrow the king by getting his son to marry Lady Jane Grey.