Complex sentence: When Mary Hemings left Monticello, she took her younger children Betsy and Joseph with her to Charlottesville, where she lived openly as Bell's common-law wife, and had two children by him.
Split into simpler sentences: When Mary Hemings left Monticello, she took her younger children Betsy and Joseph with her to Bell's. She lived openly as his common-law wife, and had two children by him.