thanks for trying to help gjaltemba !!
I am embarrassed to say my son on the other end was the one telling me that he couldn't connect to anything on the remote LAN from the home LAN. As I was troubleshooting that issue, he mentioned the internet had been acting up for "about the past hour" - this is at the home address running pfSense, and it happens to be on a gigabit connection.
After troubleshooting that issue to TWO LAN computers where two other members of the household were each downloading (and I think possibly seeding) a 3.3 GB patch for ARK (and then stopping those) - he could immediately connect to the ASUS LAN cameras web server. He isn't able to see the video streams, but I can see them on my phone across two VPN connections, so I think it must be 99% working.
Knock on wood, I think it might be fixed *