Complex sentence: The next day they "borrow" Heinerle, the son of one of Peter's friends, who soon turns the house upside down, driving the housekeeper, Frau Stadelmeier, to despair.
Split into simpler sentences: The next day they "borrow" Heinerle, the son of one of Peter's friends. He soon turns the house upside down, driving the housekeeper Frau Stadelmeier to despair.