Complex sentence: The family survived their father's regular bouts of unemployment, gambling and alcoholism with the help and support of their grandmother, and an older sister, who was employed as a PA to the London Vice President of Morgan Guarantee Trust Bank.
Split into simpler sentences: The family survived their father's regular bouts of unemployment, gambling and alcoholism with the help and support of their grandmother and, also his sister. Who was employed as a PA to the London Vice President of Morgan Guarantee Trust Bank.