Complex sentence: On the one side, her father Sir William Dormer's family (moderately prosperous landowners and wool merchants) remained staunchly Catholic, her mother Mary Sidney's family embraced the new religion of Protestantism.
Split into simpler sentences: On the one side, her father Sir William Dormer's family (moderately prosperous landowners and wool merchants) remained staunchly Catholic. However, her mother Mary Sidney's family embraced the new religion of Protestantism.