Complex sentence: The sagas they created were elaborate and convoluted (and exist in partial manuscripts) and provided them with an obsessive interest during childhood and early adolescence which prepared them for literary vocations in adulthood.
Split into simpler sentences: The sagas they created were elaborate and convoluted, and exist in incomplete manuscripts. They provided them with an obsessive interest during childhood and early adolescence, which prepared them for literary vocations in adulthood.