could you please correct me if i’m wrong, but if i’m right you have 1 BIG screen and on that screen you want to have multiple VNW instance to multiple wyse devices.
This is possible but i wouldn’t recommend it because the VNC process will use a lot CPU power on the client side. It’s just for emergency use you want to use different tools if you would like to watch/monitor/shadow the users.
Anyway if you still want to have for what ever reason multiple VNC session all in one BIG screen, have a look at TightVNC and save every config you want. After that you can just double click on the config and it will start the session, it should also be able to save your screen position.
It’s not like a thumbnail view but you can have a look at it.