This implies that God had decided that a certain number of people should be killed by their enemies. This can be translated in an active form. Alternate translation: "until people had killed the full number of their fellow servants ... sisters whom God had decided people would kill, just as people had killed their fellow servants ... sisters" (See: [[rc://en/ta/man/translate/figs-rquestion]])
This is one group of people described in two ways: as servants and as brothers. Alternate translation: "their brothers who serve God with them" or "their fellow believers who serve God with them"
Christians are often spoken of as being one another's brothers. Females were among those spoken of here. Alternate translation: "fellow Christians" or "fellow believers" (See: [[rc://en/ta/man/translate/figs-metaphor]])