Consider leveraging the filtering functionality of dashboard actions, set so that clicking on a row at any level filters all child levels. To do this, break up each level of the hierarchy into a separate worksheet and then add them all to a dashboard; then add filter actions (under the dashboard menu). Below is an example with the three measures (butchered from Superstore) shown for each level (though I only did three levels). If the measures take up too much space, then you can remove them from the hierarchy worksheets and put them on separate worksheets (one for A, one for B, as described in your post) that get filtered based on hierarchy selections.
For consistency (and ease of development), create/format/refine the worksheet for Parent Group first, then for the other levels just duplicate the finished worksheet and swap out the dimension that is on rows.