Complex sentence: She was born into an upper-middle-class family: her father, Robert Simpson Cassat (later Cassatt), was a successful stockbroker and land speculator, and her mother, Katherine Kelso Johnston, came from a banking family.
Split into simpler sentences: She was born into an upper-middle-class family: her father, Robert Simpson Cassat (later Cassatt), was a successful stockbroker and land speculator. Her mother, Katherine Kelso Johnston, came from a banking family.