Complex sentence: He was the second son of Charles Calvert, 3rd Baron Baltimore (1637--1715) by Jane Lowe, and became his father's heir upon the death of his elder brother Cecil in 1681.
Split into simpler sentences: He was the second son of Charles Calvert, 3rd Baron Baltimore (1637--1715) by Jane Lowe. He became his father's heir upon the death of his elder brother, Cecil in 1681.