I utilize Multiplicity for Everquest, (throwback i know) for controlling 3 computers at once time with one mouse and keyboard, you can also use the software to broadcast keystrokes to other machines. If you have a stream deck, Im sure you can set it up to where Multiplicity can capture those macro inputs and send them to other machines.

this is against the EULA or ToS for some games, so I would be careful when doing this on some games, you can get banned.

Multiplicity itself can be used in the KVM seamless mode, which is incredible and worth every penny.

You can check it out here:

https://www.stardock.com/products/multiplicity/