NPCs needs to have a “leashable” restraint, as of right now, either collar ropes, wrists ropes, ankle ropes or the armbinder, you can equip them all at once too.
Equip ropes in your hand, aim at the NPC to leash them, you can leash them to each other and create a line of captives following you. If you want to leash them to a ceiling hook to create strappado or suspension position, you have to create a leash from the ceiling hook first then on the NPC.
I will improve this process in a future update so you can create positions without having to create the leash from a specific object.