In the harem, why do concubines only call their sisters and sisters? What about status? If a low position is later promoted, why should she go to the low position?

Sisters and sisters usually depend on their status. When their status is high, they usually change their names. Unless there is personal relationship, the status varies from dynasty to dynasty.

If the relationship is directly bad, you don't have to hide it, or if it is official (see the low position for the high position), you should call the title (Empress X, etc.).