I'm having trouble finding information on this issue because the keywords are very similar to assign one task to multiple assignees. My issue is assigning multiple tasks to one person with one mention, as shown below. ("site office manager" will be edited to @mention a specific user)

In a perfect world, this format would assign each of the child tasks to the parent task assignee and the parent task would be automatically completed once the child tasks are all completed. I realize that we don't live in a perfect world. How close can I get to perfect? (preferably natively, but I will consider suggested add-ons or user macros)
Thank you!