Complex sentence: He moved back to Bangladesh a few years later at the age of nine due to his fathers concern of different cultures and the possibility of losing their Muslim identities, however they returned when he was at the age of 13.
Split into simpler sentences: He moved back to Bangladesh a few years later at the age of nine due to his father's concerns about different cultures and the possibility of losing their Muslim identities. However, they returned when he was at the age of 13.