그들은 함께 살고 있었다
이건 they were living together 아닐까요?
I think you are right, Philo. To me살고 있었다 indicates the condition at the time in question,which we would translate "were living..." "Had lived together" implies they were no longer living together at the time being referenced.
그들은 같이 살고 있었습니다 틀린가요?