Complex sentence: In a brilliant set of marriages, Agnes was therefore married to Laurence Hastings, 1st Earl of Pembroke, a ward of her father's, while her sister Beatrice was married to Edward, 2nd Earl of Norfolk.
Split into simpler sentences: In a brilliant set of marriages, Agnes was therefore married to Laurence Hastings, 1st Earl of Pembroke, a ward of her father's. Her sister Beatrice was married to Edward, 2nd Earl of Norfolk.