In visual matrix, how to show multiple dimensions in the same row keeping grand total

Hello,

I'm having trouble trying to create a matrix that shows multiple dimensions in the same row and the grand total of every column.

I have created the following dummy example to better explain what I need:

https://drive.google.com/drive/folders/1qK7o-A0OS4nlqtxTOvy45ucmj0BFo5v_?usp=sharing

My tables:

My goal is to create a matrix like this, but what I want to solve is that I can't get the way to add the total of every column:

I need to show:

Total: 923 / 729 / 310

If I create a default matrix visualization, I don't have the dimensions "seller_id" and "seller_name" displayed in the same row:

Then I chose to deactivate the "stepped layout" option and got something like this:

But I had to deactivate the "row subtotals" option because I don't want to show those subtotals in the middle. However, by deactivating that option, I can't figure out a way to display the final total that I want to show.

Thanks in advance!