Complex sentence: Finally the alarm was raised in March 1920 by Amundsen's brother Leon when he got a telegram from his brother, who was wintering then near Ayon Island, enquiring whether his men had reached home safely.
Split into simpler sentences: Finally the alarm was raised in March 1920 by Amundsen's brother Leon when he got a telegram from his brother. Amundsen, who was wintering then near Ayon Island, was enquiring whether his men had reached home safely.