Hi there Emma, that is possible depending on how many dependencies you are attempting to set up (from my experience). Have you looked at how to set up lead/lag time with the dependency types? Are your dependencies strict or flexible?
We agree that being able to set dependencies between items and subitems (not just the same level) would be really helpful for managing more complex workflows. This is a current limitation, and we’ve shared your feedback with the product team for consideration in future updates.