Need help with optimizing network - QoS

[AMDGrill]

As title says, I'm but a rookie when it comes to networking, so let me sum this up:
A Zyxel VMG8324-B10A router provides civilization and freedom to my home, with a tiny bit of 35mbps connection.
3 Gaming computers are hooked up to the ethernet ports of the router. 
Various wireless devices are connected to the router.
Sometimes, guests connect to my network, jump to YouTube, and put on a 1080p video, watching it from a 5" screen, which ultimately results in my network bandwith getting sucked, my ping getting high, and my gaming / watching experience ruined. 
What I want to do is:
Prioritize Ethernet traffic over any WLAN traffic. 
Limit WLAN Bandwith
Prioritize certain WLAN devices over any other WLAN device, if possible.

Router supports basic QoS as far as I can see. 
And dd-wrt doesnt have my router supported--but then, I wouldnt be able to go through all the settings with my tiny knowledge even if it did.
Long story short, if it's not too much of a hassle, could I get some help accomplishing said goals?

 

All these settings are default

[BloodKnight7]

Hy man! I dont know your situation but my recommendation would be to get a netgear router and follow this procedure https://kb.netgear.com/24266/How-to-enable-Quality-of-Service-QoS-on-routers-with-NETGEAR-genie , in reality most of the more commercial brandes (d-link, asus, linksys, etc..) will have this functionality for home users (point and click), to be honest I have never seen this Zyxel brand before so I cant be of much help with their GUI.

 

Best regards.