bless

Yes

I would get a domain name and use ddns to update your rotating IP. Then I would setup wireguard VPN in split tunnel and have your parents network tunnel back to your piholes for dns resolution.

I use cloudflare API for ddns updates but there are plenty of choices for that. If you're using cloudflare for DNS just keep in mind you can't proxy the DNS entry for the ip for your VPN host as CF only forwards traffic over certain ports and they are not configurable (on free plan anyway not sure about paid).

Don't get rid of it, install Kodi and/or Plex on it

+1 for dst nat on googles dns servers back to my piholes

Ditto

The error is telling you you already have something listening on port 80 so docker is unable to bind to 80 again until that is released. Try disabling nginx and apache as you stated.

You can run

netstat -pln

to show you what's running on what port on your host is you want to verify

Yea I should read better

For infrastructure critical services I recommend reservations on the DHCP server and then set static assignment on the device for the IP reserved in DHCP. This way if the device ever fails over to DHCP for any reason the IP will not change. I'll usually also leave some small address space outside the DHCP scope available for static assignment if needed, usually at the front and usually around 20 IPs max as it's easier to let DHCP do the heavy lifting.

Static IPs are important on infra critical devices if you ever find yourself in a situation where the DHCP services are not available, you don't want them to be a single point of failure.

Just my 2 cents.

Better to set the DHCP server to hand out the dns rather then set it device by device

Wait till you plug in your cell phone to charge they start calling home like crazy

To each their own!

Check out prowlerr over jacket, I found it much better