Complex sentence: Jiro is one of three brothers (the other two are Ichiro and Saburo) who all fall in love with the 19-year-old Melmo, and is the one that Melmo picks and eventually marries.
Split into simpler sentences: Jiro is one of three brothers (the other two are Ichiro and Saburo) who all fall in love with the 19-year-old Melmo. He is the one that Melmo picks and eventually marries.