The 2nd and 3rd nodes are completely wireless accept for the power cord. You will need to utilize the Linksys App to set up the additional nodes, but you can place the nodes anywhere that they are in signal range of the "parent" node.
In theory, if your neighbor is fairly close such as an apartment or suburb housing development, then yes, it could be possible to place a node in their home and make it work. I am sure, however, this uses is not the intent of the developer.