correct or incorrect...?
you can only use one ps2 device at a time per port...
Ummm....it depends?
If such a device existed (it may, I don't know), a "hub" is theoretically possible. It would act as a traffic controller for multiple devices. Similarly, a "pass-through" device could be chained for the same end result, but would impose delays proportionate to the position of the device in the chain.
But if you are talking about hooking 2 keyboards to a single PS/2 port with a simple passive splitter, no, it won't work.
RandyT