It looks like you just want a collapsible subsection for reach row in the DG2. For the column where the button is, make it a custom content column, and put a group box widget in there, with your content/listview inside the group box.
Collapsed:Expanded:
Then you can apply some classes with styling to apply spacing/expand the whole row as needed when the button is clicked. Note that this is probably a bit easier from a styling perspective when done with a list view as the parent as well.