im not exactly clear on what you want to do. Are the other two PC's also Citect nodes?
If so, the best thing to do is keep your original Citect PC as the IO Server, and configure the other two citect PC's to be clients of that IO Server (ie in the citect.ini file, set the [Client]Primary equal to the server name of the IO Server).
That way only the original Citect PC will be interrogating the PLC, the other citect PC's will just talk to the Citect IO Server.