Complex sentence: Her brother was Quintus Caecilius Metellus Nepos, a former consul whose stepdaughter Mucia Tertia was now wife of Pompey; her cousins included Quintus Caecilius Metellus Numidicus Pius, chief ally of Sulla.
Split into simpler sentences: Her brother was Quintus Caecilius Metellus Nepos, a former consul whose stepdaughter, Mucia Tertia, was now wife of Pompey. Her cousins included Quintus Caecilius Metellus Numidicus Pius, chief ally of Sulla.