So it sounds like you want some automation that will create all of these sub tasks. And then you want the parent test to close when all the sub tasks are complete. Is this correct?
Assuming so, then you’re going to want to have some sort of scripting or automation to create those sub tasks for you. As I am on cloud I happen to use automation for Jira. Which is available as an addon for server. In cloud they have some templates that are you specifically for on-boarding new hires which may or may not meet your needs. Regardless of having an available template you can easily create them yourself. One thing you mentioned was that this would all be kicked off as part of an email. That makes things a bit more challenging as it relies on specific text in the subject or body such that automation could parse as part of the rules Condition to know when to create the subtasks.
There are other add-on solutions that could achieve the same thing such as scriptrunner.
The final part is to close the primary task when all subjects are complete again that can be done through automation or scripting add-on.