Anki will use the display order from the deck you select to study, and not any subdecks it may have.
The subdecks’ order do not matter (if it did, how do you think Anki will behave when one the display orders were different). What is the display order in the parent deck/the deck you’re clicking on to open review screen?
If the deck you’re clicking to study has the correct sort order I don’t believe you need to do anything else. What are you seeing when you click to study from the deck?