So I have tested the idea of setting up the two RPis, one (Astroberry Red) as a Hotspot (2.4GHz for the AZGTi) and the other (Astroberry Blue) as a client on the Astroberry Red network. From my laptop connected to the Red network I can VNC into both RPis simultaneously. Red has only the Hotspot connection defined, with the fixed IP address 10.42.0.1. Blue has two options, Hotspot mode with fixed IP address 10.42.1.1 with priority -99 and as a client on the Red network with priority +99. The first time I switched on Red then Blue with a monitor attached, Blue connected as a client as I could check on the monitor. However since going headless again, Blue always sets up as its own Hotspot so I can see the two networks on my Laptop connections list, plus also the AZGTi (192.168.4.1). I am not confident that the priority levels selection actually works - I have had problems before where an RPi would still set up its Hotspot when close to the home WLAN with higher priority setting. I am running each RPi booting from SSD so there is always an active USB3.0 port which I guess could be adding interference into the mix. I will try again with SD cards instead of SSDs to try to eliminate some issues, but any thoughts on any of this?