I want to monitor my 4 devices on the router level. My settings look like shown in the picture UPnP.jpg. (I don't succeed in attaching my picture Help needed)
Does this work, or must my router support SNMP?
Sorry there isn't much I can say specifically about your situation without seeing your screenshot.
To add the screenshot you can either attach it to your message via the "Attach a file ..." link all registered users have right above the message field; or upload it to any online image hosting service you like (for example, tinyimg.io) and simply add the link to your message.
Here is some general information about router monitoring:
If your router supports so-called SNMP or UPnP protocol, you can monitor all traffic via your router. This will not give you a per-device usage breakdown and the monitoring computer must be continuously on to poll the router and collect usage data.
Usually SNMP monitoring is more reliable as router firmware often contains bugs in their UPnP implementation. Most common issues are stopping monitoring after hitting a 4 GB (2^32) mark or simply incorrect usage figures.
This help page on router monitoring provides further details. If it works - great! But if not, I am afraid there is nothing we can do - some routers just don't properly support monitoring.