Im about to setup a local dns server and a proxy server in the same machine (A raspberry pi). It will be connected to the network just like all the other computers, through a switch. The switch is connected to a router (And I have several devices connecting to the router through wifi). I will disable the router's dns and use the local one

I need to make sure that all the traffic pass through the proxy and my dns server. Even if someone manually edit the dns in their machine. Is this possible? How can I do that?

Please note that the wifi router doesn't have complex features. Its provided by the ISP and I don't have a way to replace it because I use IPTV and it use the same router and the ISP doesn't allow us to change those settings.

For the DNS it's quite simple, you only need to define your local ip as only dns server (it's in /etc/resolv.conf)

For the proxy, I am wondering if you really mean proxy or router/forwarder.
You could define this same Pi machine as gateway for all other computers, or you could put an HTTP server on it as a proxy server. It depends on what you mean by proxy.

You will also have to pay attention to the route table on all machines (route command) to make sure packets are going to the Pi when they are supposed to.