Re: It's been years since . . . .
I have a newer hub supplied by BT which doesn't allow the user to change the DNS settings. However, it does allow you to turn off DHCP which stops those DNS settings being used by the rest of the network.
I've then got a Raspberry Pi running Pi-Hole which although ostensibly an advert blocker, also includes a DHCP server (earlier versions didn't, but it's all integrated into the UI now). This allows everything on my network to get DNS lookups handled by Pi-Hole, and only the BT Hub looks up whatever it needs to on BT's DNS servers.