How do I monitor how much bandwidth each device on my WiFi uses?

[StrandedonEarth]

Lately my family of 5 has been shattering my ISP's bandwidth caps. I would really like to know where it's going, between 2 laptops, 2 smart-TV/BR's, and a pile of iCrap. I'm sure the biggest users are NetFlix and YouTube. My router is a Motorola/Arris SBG6782, which doesn't seem to mention SNMP monitoring (the SBG6782-AC does). I'm trying PRTG right now, but it's kinda complicated and probably overkill for my needs. I tried setting it up before I realized my modem/router doesn't support SNMP, but PRTG has a zillion other options to try.

So if someone could suggest an easier way to track bandwidth usage on my network, or how I can set up PRTG in an easy-to-use, low-overhead way, it would be greatly appreciated. Thanks