Ah, the win task manager has a data rate meter. This I will check our Sir Paladin, where ever you are roaming. Thank you.
All devices have to be at least temporarily networked through some choke point that has measurement capabilities.
In my case at the moment that is a Desktop running Linux. The desktop is equipped with both an ethernet connection and a wireless card.
I set the wireless card to be a hotspot and make sure all wireless devices are connected to that. Then the vnstat program/command/service on the desktop collects total house useage. Then if everybody is behaving, we go back to a Wild West Wireless.