VPN tunnel between two houses?

My mother and I live in separate residences, served by separate ISP connections. They’re too far away (8 miles and mom’s condo has an HOA that restricts outdoor antennas.) from each other to WiFi between the two.

I’d like to be able to initiate a remote desktop connection to my mom’s computer.

I’d like her to be able to connect to my NAS/File Server.

Basically, I’d like her computers and my computers to appear to be on the same local network.

How can I accomplish this?

FWIW, We CAN both have the same ISP (Verizon FiOS) though she is currently on Xfinity/Comcast, much to my chagrin. And I can use OpenWRT on her router, though, she currently uses the Xfinity/Comcast supplied hardware.

OpenVPN TAP, running on 3rd party routers.

Tailscale is the easiest and free for personal use. OpenWRT can run Tailscale in which case you can tunnel her whole subnet, and you can tunnel whole subnets on both ends. But easiest is just to run Tailscale on every device you want to access or access from.

Make sure you’re not both running the same IP addressing on your internal networks at both places. Nearly every router assigns 192.168.1.0/24 to the LAN, and if both are assigned the same network, your VPN tunnel isn’t going to work. Change the other LAN something like 192.168.2.0/24 or something else.

Don’t forget about upload speed. If her Comcast is anything like the Spectrum available in my area (I have Metronet) her upload speed will be about 20mbs. And when you are accessing her side of the network, her upload is your download.

She will have Verizon FiOS. I wouldn’t let my worst enemy use Comcast / Xfinity.