Hi @atboss,
At this time it is not possible to connect the due dates of subtasks to the due date of their parent task. There are a few workarounds and alternate solutions that I think will work for you, though.
I recommend that you consider converting your 12 subtasks to tasks. Tasks offer the flexibility to adjust due dates, move actions around, add custom fields, etc. I suggest you visit this thread on adjusting multiple due dates for tasks, which I think will provide a solution for you: How do I set Asana to automatically trigger due date creation upon completion of other tasks? - #2 by Alexis
We have lots of interesting discussions about tasks, due dates, and subtasks that might interest you. Here’s a start:
https://forum.asana.com/t/change-due-dates-of-multiple-tasks/5949/3
Please let us know if you have follow up questions