You can't disable IPv6 on the Google fiber router or set a range. You can only do that with ipv4 which I'm not having a problem with.
The Pi hole is set as the DHCP server. If you enable or disable IPv6 on the Pi hole DHCP it will default to using IPv6 on the Google fiber then (For some select devices). So if possible I would like to block the Google IPv6 DNS addresses at the firewall on the raspberry pi.