How can I get Multiple Insert, Update, Delete with MRT all working together??

I have a 3 table db that includes a Category table, Sub Category table and a relational table (see 1st image).

I then have an insert, update, delete multiple records for both the Category and Sub Category table. This works great. (2nd image).

The insert/update/delete fields are in a repeat selection, similar to an example I saw for the BlueSky admin. This works just fine.

But I needed to take it further.

When inserting the Sub Category, I need to also insert records into the relational table so that each Category is related to the Sub Category. I have this working by using the Manage Relational Table behavior and including a multiple select in the Sub Category form that is dynamically populated by the Category table. (But I had to use a single record insert within this part).

Here's my problem. I can't figure out how to delete the records from the relational table at the same time the records are being deleted from the Sub Category table.

Do I add a second MRT behavior? or a second Delete Behavior?

And one last thing. In the MRT the key value is the "key value set to the session variable declared in the Single Record Insert server behavior". But what do we use in the MRT for a multiple record insert behavior?

Thanks,
TroyD