Complex sentence: These new experiences made them grow as people, and thus they were no longer true duplicates, so the three merged into one being and were exiled, and she/they soon joined the Legion as Triplicate Girl.
Split into simpler sentences: These new experiences made them grow as people, and thus they were no longer true duplicates. So the three merged into one being and were exiled, and she/they soon joined the Legion as Triplicate Girl.