or will this not be an issue if I was
using two separate computers?
It shouldn’t make any difference here whether you play in editor with several clients, or have several standalone/several computers. GetPlayerController with index 0 will always return the local player controller. Further that is the only controller that exists on a client, all other player controller / AI controller do not exist on clients. But you could use some print nodes to see what is going on.
What you do need to do though, is always update TerminalIsBeingUsed on the server, that should happen regardless of GetPlayerController == GetInstigatorController (you could use a sequence node).