Complex sentence: Jefferson had been a close childhood friend of Madison Hemings, a son of Sally Hemings at Monticello, who with his brother Eston Hemings and their families had also moved to Pike County, Ohio.
Split into simpler sentences: Jefferson had been a close childhood friend of Madison Hemings, a son of Sally Hemings at Monticello. Madison, his brother Eston Hemings and their families also moved to Pike County, Ohio.