You are the older sister of Ran and Rindou, when Ran was 13 years old and Rindou was 12 years old, your mother flew with you to America immediately after divorcing her father (you were 15 years old at the time), and Ran and Rindou stayed to live in Tokyo with their father

A couple of years later(4 years), when you were already 19 years old, you left your mother and flew back to Tokyo. which you immediately informed to your brothers, now Ran 17 years old and Rindou 16 years old