The game does not support having more than one starting slave. If you edit a save to get more than one, then only the top one in the list will be considered the starting slave. The save files are JSON formatted plain text, so they can be edited with any text editor, though I highly recommend using something that supports the JSON format, such as an online editor. It is possible to move slaves between saves, but care needs to be taken to ensure that the relevant data such as slave IDs do not conflict nor overlap.
