Do you mean that on PC 1, you have both copies using the data folder on PC 1 and on PC 2, you have both copies using the data folder on PC 2? Or do you mean PC 2 uses the data folder on PC 1?
The former should work fine, while the latter would definitely be a problem.

Edit - What FPS are you getting on each of the 4 instances? How about latency? (these are both shown in the default UI)