Due to the way BP has been re-designed for easy theme compatibility, most times BP will use your theme's templates (including those with sidebars) for its own BP pages (like Activity). But if your premium theme has a non-standard page hierarchy there could be a problem. That's why it might be good to get in touch with the theme author about this before pulling out any more hair. Maybe he can give you an easy fix?
Also I see that you have some plugin like 'BP Activity Widget' that hasn't been updated in almost a year and a half, which is too long for use with something like BP. Check into that?