Complex sentence: After the death of his last surviving child, Charlotte, nine months after she married, he co-operated with Elizabeth Gaskell on the biography of his daughter, and was responsible for the posthumous publication of Charlotte's first novel "The Professor" in 1857.
Split into simpler sentences: After the death of his last surviving child, Charlotte, nine months after her marriage, he cooperated with Elizabeth Gaskell on the biography of his daughter. He was also responsible for the posthumous publication of Charlotte's first novel, "The Professor", in 1857.