Hi,

The connection between the machines happens through Aximmetry. Aximmetry basically syncs what you do in Aximmetry for each multi-machine. Except in cases wherein the Flow Editor module(s) determine that only machines with a specific id should execute certain nodes.
Unreal is not fully synced internally between the machines.
You can send videos from one machine to another through NDI connections. However, note that multi-machine are designed so that each machine has an input and output. It doesn't send every rendered video to the "Main Server" and the "Main Server" doesn't output every rendered video. "Main Server" only outputs the video that the "Main Server" renders.

We strongly recommend against it but you can use Live Sync while being in a multi-machine. However, the Unreal Editor will have to run on each machine and any change you make in the Unreal Editor at a machine won't affect the other machines.

We suggest using the cooked mode. You can set up Unreal blueprint logic for any changes you want to make while your Unreal scene is running. And when you trigger these blueprints from Aximmetry, they will affect every machine.
Like the trigger in this tutorial: https://aximmetry.com/learn/tutorials/for-aximmetry-de-users/passing-trigger-from-the-unreal-scene/

Warmest regards,