@Jmbhome,

Is his phone connected to the same network that your phone is? Or, if you disconnect from the Wi-Fi, do the cameras appear as offline?

Is his phone using the same account as your phone, or is it his own account that you have shared devices with?

It's possible that the cameras have lost their connection to the cloud and are only communicating with your phone via Wi-Fi. While rebooting your router should have solved this, try rebooting the cameras. You may also consider changing the DNS server of your network to a common service such as Google or Cloudflare, if it is not already.

I would also check to see if there are any VPN settings enabled on his phone that could be interrupting his phone's connection with the servers.

Lastly, try connecting his phone to the same network as the cameras and seeing if the cameras then show as available.