Horrible Wi-Fi ping if 2+ people use it

[Dokiloki6]

The router model is ZyXel VMG5313-B30A and this is the problem I have.
The internet is not owned by me, details of that are not required just that I don't have access to connect with ethernet but I do have full unrestricted access to the router via my computer.

The problem is that I don't understand how it works. The only way for someone to be using it is to get full bandwith or nothing. Example: if I run a speedtest on my computer while my girlfriend is playing League she will get a ping spike over 1700 during that time and my ping will be around 40 which is the normal average. If she played league and I played wow, she would get around 200-600 spikes while I would get 800+ consistently.
The speedtest always gives me full bandwith, but to have it I must continuously run it, even though I set up the QoS (not sure if correctly) to give me all the bandwith when I run WoW which you can see here https://image.prntscr.com/image/Y2cA-EFDQRq0-cnB4yHcqg.png.
The speedtest result is always the same when I run it https://image.prntscr.com/image/pnL5RqXeRZOSQVuvE5gknA.png.
My question is what the hell is going on, 34mbps should be enough bandwith for both of those games easily without any hiccup, and why isn't my QoS working?

 

[Kewlx25]

Latency is not caused by a lack of bandwidth, it's caused by too large of buffers. Even a 1Mb connection should never have more than 50ms of latency.

You have two potential issues where one or both are affecting you.
1) Buffer bloat. This is more difficult to fix because it requires much greater technical knowledge until anti-bufferbloat queuing becomes common.
2) Cheaper or older wifi access points can have very unstable bandwidth or latency when more than a single device is using it at the same time. An example of a good access point that won't break the bank: https://www.amazon.com/Ubiquiti-Unifi-Ap-AC-Lite-UAPACLITEUS/dp/B015PR20GY