Complex sentence: The school also has a brother school, Mazenod College, with which they provide events, so that the girls get to not only work along girls but also have the opportunity to work and interact with boys their age.
Split into simpler sentences: The school also has a brother school, Mazenod College. Which they provide events, so that the girls get to not only work along girls but also have the opportunity to work and interact with boys their age.