Best way to set up NextDNS - router or PC ?

Really sorry, but I am new to this and not terribly techy. I am trying to stop my 87-year old father being scammed and I believe scammers have taken remote control of his PC and set him up with a Revolut bank account so he can send funds to them. He has already sent over £25,000. He is in hospital at the moment so I can get onto his Windows 10 PC tomorrow and install NextDNS (which I have already set up here at home having watched a very useful YouTube video.).

Am I better off putting the NextDNS DNS server addresses into his EE broadband router (I am in the UK) and will that then trap his iPhone and iPad aswell whilst he is at home on his WiFi ?

I'm assuming if I set all this up on his PC it could be undone by someone who gains access to his system (by using QuickAssist perhaps ?) whereas they would not be able to get into his router (as I will change the password when I am there). I have blocked all the remote access software domains I can think of but from what I have read this would not stop Quick Assist.

Sadly he is complicit in this scam, I cannot make him understand that it is a scam, and nor can the police. So I need to do this without his knowing and without him being able to bypass it.

Appreciate any help.

Many thanks

Stephen