Can anyone help me get the metadata to fix the sorting in iBooks and synchronize it properly via Finder?

Hello! Anyone encountered this issue in IBooks? I want to try to sort my audiobooks in iBooks in a way that it is easier for me to check all of the books in a specific series. In my Mac, I am able to select which audiobooks I can synchronize either to my iPhone or iPad. What I want is to be able to sort through all these audiobooks based on the Series it has and not the specific book title (i.e. Hunger Games Trilogy, Inheritance Cycle, Harry Potter, etc.) To further illustrate, in the Audiobooks Tab of Finder for my specific device, I'd like to be able to see on the Audiobook part the name of my designated grouping - say Hunger Games Trilogy, when I click that, the Part column should show all 3 books associated with it. |Audiobook|Part| |:-|:-| |Hunger Games Trilogy|The Hunger Games| ||Catching Fire| ||Mockingjay| Now this can be easily solved by changing the metadata of each audiobook Album tag to "Hunger Games Trilogy" The problem now lies is how it is displayed when I view it in iBooks app in my Mac, iPhone or iPad — it will only be just one entry — which would be Hunger Games Trilogy. iBooks seems to render all the audiobooks as one item. **Is there a metadata tag I can fill up to make sure that iBooks still treats each of these audiobooks as separate items instead of one?**