The term for combining their computational power is "concurrent computing", "parallel computing" or "distributed computing" which aren't really all exactly the same but i can't find distinctions betwen them that are well defined. making them all accesible in one place is something i want to do as well but i get distracted easily and haven't made much progress.

KVM is an abbreviation that means 'keyboard video mouse' which also might be something to look into but it can be confusing as it also is an abbreviation for 'kernel virtual machine' which also might be related but that's as far as i got mostly.

i believe you can create a local network if you have a router/hub/switch device with multiple ethernet ports. if all the devices have wifi you should be able to connect through that, using something like jellyfin or maybe proxmox. wish i knew more and could help, hopefully you get better advice because i want to do the same or something similar.