As one what exactly? From what I think you're trying to say, your best bet is to plug all the NASes into one router, which connects to the rest of the network.
Are you saying you want link multiple NAS devices and make it appear as one big drive when you open it in other computers? If so, then it is probably impossible to do. The sheer latency of data going through the network might fool your controller into thinking that the drive/NAS might be dead.