Welcome, @Matilda_Schieren,
What’s best for your needs would depend, but here’s one option to consider.
Have a Content (meaning Content Topics) project with a task for each title.
Add a subtask if there’s a written version.
Add a subtask if there’s a video version.
Multi-home (add to project) the subtasks, not the parent task, to your Editorial Calendar project.
Optionally, you could also have a Written Content and a Video Content project where you’d multi-home the parent task to either one or both. These projects could add content-specific custom fields.
This eliminates sub-subtask, and any parent or subtask is always just a click away from its relatives (via the right-side Task Detail pane).
For more about workflows, consider my free workshop video:
Thanks,
Larry