First thing first:
Set a static IP on your raspberry from the same range that your router is providing DHCP ips:
https://www.raspberrypi.org/forums/viewtopic.php?p=1070893#p1070899
Then, run a pihole -r and reconfigure.
Make sure all the IPs are matching and everything is updated.
After that, make sure Pi-hole is set-up to respond to the interface that the request is coming on (I'm assuming this would be eth0 in this case ).
Once set-up like that, your raspberry will retain the IP and it will be easier to use that, as it survives reboots and always stays the same.
Once you are done with those settings, make sure you use the raspberry IP (the one you specified in /etc/dhcpcd.conf), as your DNS server on your clients.