Hi @Connor_Briggs,
Here is a helpful post on how to debug your issue:
You can also use the new Import Hierarchy
option when importing your NPC model. That way you will get the full bones hierarchy and you can easily drag and drop an entity as a child there. That way you can do the same thing without code.
https://developer.playcanvas.com/en/user-manual/assets/import-pipeline/import-hierarchy/