Main Quest: Yuga Kshetra

NPC Servant Update: Throughout this Lostbelt, NPC Servants will have CE equipped. Most of them do not have a name, and cannot be moved to your servants. (The CE will stay with the NPC)

For certain quests that have fixed party setup, for example "having certain NPCs in your party, or just them alone", in the past, players are not allowed to switch the position of the servants, but as of Yuga Kshetra update, now you can move them around.