How do I setup RTSP proxy to advertise to HLS proxy running on another server

[Admin]

Help a newbie? I would like to have an RTSP proxy running on a Raspberry Pi advertising to an HLS proxy running on a server. I noticed the HLS proxy has a -R "REGISTER" flag to listen for an advertised RTSP stream, but how do I configure the RTSP proxy to advertise?

Here's why: I'm building a chicken coop monitor product based around a Raspberry Pi called SecureCoop that I'm hoping to sell soon. I would like to include connectivity to IP cameras to monitor the coop, but do so in a way that requires no setup for the customer. They plug in the cameras and it's instantly available on the iOS/Android app. No opening ports in the firewall. Due to privacy concerns, the cameras must be protected by encryption, username, and password. And the solution should be (eventually) scalable to a few thousand simultaneous users.

So I'm thinking of this kind of setup:
[IP cam RTSP]<--[RPi Live555 RTSP proxy]-->[OpenVPN]--[Home firewall]--[OpenVPN]-->[Live555 HLS proxy]<--[App]

The RPi would have a DHCP server for the cameras.

Here's an image in case my ASCII art does not come through:
https://i.imgur.com/DAmbUX1.png

Or is there a better way to handle this?