I think that one should consider the possibility of FB group indirectly accessing this data.
They don't have to collect information only directly from their FB/Instagram/WhatsApp apps: what they can do is buy information from other companies that publish thousands of "free" apps on appstores.
You have to wonder how so many of these free apps seem to sustain themselves since GDN advertising does not seem to be profitable enough.
FB group should be obligated to disclose whether they are buying information from these kinds of third parties.
More importantly they should disclose whether the price they pay is illogical, effectively making them silent partners in an indirect scheme to access your camera/mic information, while at the same time maintaining the allegation that "we do not access your mic through our apps".