I’m sorry, Dynamic Widgets does not change CSS. It only shows or removes widgets from the sidebar following the rules you have set. The showing and hiding of widgets is NOT being done by using CSS or HTML.
When something goes awry when a widget is removed, that means most of the time one of the widgets remaining is not coded correctly. A closing div is missing for example. It seems by the way the CSS problem only occurs on the main Groups page. Within the groups everything looks OK.
I’d also suggest to close the guest account you have created immediately. This Forum is public, so everybody can see this and everybody is able to log into the site now.
Now, back to the original problem. You were not able to control the widgets within hierarchical groups, because of the use of BP Group Hierarchy. That should be possible now.