Complex sentence: His fluent German certainly made it much easier for him to blend into the local populace, yet he refused to attend the lectures for the duration of the war to avoid difficulties, but his professors then offered to tutor him in their own homes.
Split into simpler sentences: His fluent German certainly made it much easier for him to blend into the local populace, yet he refused to attend the lectures for the duration of the war to avoid difficulties. His professors then offered to tutor him in their own homes.