It is not possible to delete all the related records via a single endpoint. For this firstly you need to get all the related records of the module via using /<module>/:record/link/:link_name GET and then need to delete all and then at the end need to delete the parent record.
Let me start by saying that I do not normally recommendation deletion of records. It is often more useful to mark them as Inactive so user can see still the history.
Depends upon your actual business use case, there are a few options but all will require coding:
1) Create a custom API end point for this.
2) Use a logic hook on the parent module that will perform the clean up on a before_delete/after_delete event.
3) Use a custom job/scheduler task to do this on a regular basis.
