Orbi RBR850 + 3x RBS850 in AP mode with an existing UniFi router

Hello CrimpOn, by reading your post I found exactly the description of my issues as I attempted to integrate a Orbi RBR850 + 3x RBS850 in AP mode with an existing UniFi router. My configuration is:

1. RBR850 is directly connected via its WAN port to one of the UniFI router UDR7 LAN Ethernet ports
2. one RBS850 is wirelessly connected to the RBR and it is visible in the Orbi app
3. Another RBS850 is connected via Ethernet to the UDR7 and it’s NOT visible in the Orbi app
4. another RBS850 is Ethernet connected to an unmanaged TPLink switch which is then connected to the UDR7 via another of its Ethernet ports.

The screenshot below shows how the Orbi network appears on the app. Basically only the wireless satellite is recognized. All satellites work and have devices connected to them however the mesh roaming feature doesn’t happen with the wired satellites and I get connection issues when devices roam from the RBR to the wired satellites.

I have tried to connect all Orbi devices (RBR and the two wired RBS) to the switch and then the switch to the UDR7 but in this case the two wired satellites would be visible and the wireless one would disappear and never connect to the RBR (permanent blue light on the wireless satellite). Also, In this case I have used the LAN port on the RBR instead of the WAN, as recommended by Netgear with no advantage.

Based on your deep understanding of the Netgear network topology logic, do you have a better recommendation on how to configure my network? 
I need the UDR7 as a router because I have more than 100 network devices and the Orbi doesn’t perform well in Router mode. However I would like to keep using the Orbi system since I paid $1200 for it just to realize that it isn’t performing well with large networks….

thank you.