To get Emily and Tisha you can either trick Tisha into trading places with Emily and keep her anyways, or you can send Emily away with Tisha and give them gold and food when they go. To trick Tisha you need to brand Emily and not raise her loyalty. Keeping Emily in the first step when Tisha appears will immediately end the quest for Tisha.
Basic walkthrough: https://strive4power.fandom.com/wiki/Tisha_Hal