THIS is what's taking over your DNS requests.
You have a few options here.
Option 1. Manually specify 192.168.1.76 as your ONLY dns on the clients
Here's why:
Option 2. You can see if you can use the DNS setting in your 192.168.1.254 and specify the IP of Pi-hole as your DNS.
Option 3. You can try to disable DHCP in 192.168.1.254 and enable it in 192.168.1.76 (Pi-hole) and let Pi-hole manage the DHCP settings (that way, everything that connects to the network will get the Pi-hole IP as it's DNS).
Option 4. If 2 and 3 are not available, you will have to tweak the DHCP settings in your 192.168.1.254 and then use option 3 ... something like this:
https://discourse.pi-hole.net/t/swapped-to-new-router-please-help/18602/13?u=ramset