Two things spring to mind that can cause in game latency:

Your graphics card is struggling to process all your clones and creating interface lag.... not sure if this effects the latency status though.
Second if your running all 3-4instances from a single wow dir on a single harddrive then the read times could be causing lag.....

Do you notice any lag on your network in general between your computers? Run a ping from 1machine to each and see what sort of response times your seeing as it could also be that your network card drivers are incorrect of need updating.

Anyhow check out the above report back with any findings / tests you do and well go from there