When you tried using your phone’s hotspot instead of the regular Wi-Fi router, was the Wi-Fi router still powered up? What happens if you set the credentials on your phone’s hotspot so that it matches the SSID and password of the Wi-Fi router, then power the Wi-Fi router down (so that the Cam OGs basically see your hotspot as providing the same network they’re already using), and then use the iPad to attempt an individual Cam update while the iPad and Cam OG are using your phone for their Internet connection? Attempting it that way, you don’t have to go through Cam OG setup again, and if that gets the firmware updated then you can just turn off the hotspot and power the regular Wi-Fi router back up when you’re done.
I’ve never used one of those Verizon 5G Home Internet receivers, so I don’t know if that’s the problem or not, but I think attempting to bypass that seems reasonable if you don’t currently have any way to change its settings.
This seems really frustrating for you and your family member, and I’m vicariously frustrated just reading about this.