Automate dependencies and dates

When I create a new item, I’ve set up an automation to add subtasks but I want to be able to assign a due date based on the parent due date and automatically connect the dependencies.

So automate:
add subitem x at 10 work days before parent due date
add subitem y at 7 work days before parent due date and set x as a dependency
add subitem z at 3 work days before parent due date and set y as a dependency

It seems silly that you can’t automate dates for subitem based on the parent item date but I can’t figure out how to automate a date to anything other than “today” or a specific unchanging date. I tried doing it with IF statements which kind of works but then you can’t display those dates in a calendar view and I can’t figure out how to set the IF statement to include everything that needs to be in there to make it really functional.