Actually, I think this might not be the right forum for your questions. Your main concern is
I don't know which software/script you use to turn your RPi into a Hotspot but I would start looking for help in their respective forum. Maybe even an Ubuntu forum.
After you figured out which software the Hotspot really uses, try to solve the port conflict.
DNS runs on port 53, so Pi-hole really needs it.
If your Hotspot uses dnsmasq your could add -port=0 to the dnsmasq config files to disable DNS functionality and only leave DHCP.
https://thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html
Did you try to search this forum already? I know other users have turned RPis into access points along with Pi-hole...