It sounds like you’re asking couple of different questions here, but I did want to just tease one thing out.
It is possible to have events from one hub trigger actions on another hub that have two separate locations on your account, but you have to use webcore for this, and there will be some additional delay, maybe a couple of seconds. And you have to set up proxy virtual devices and do a bunch of other things. But it doesn’t add any additional cloud layers. So I don’t know if you would be interested in that or not.
This is briefly discussed in the how to article in the community – created wiki on automating an outbuilding. Which also discusses some other options.
http://thingsthataresmart.wiki/index.php?title=How_to_Automate_an_Outbuilding
Second, if what you really want to do is have multiple units in an apartment building each with their own hub, there is a community member who is running a multi family unit with 200 hubs and his company has created their own umbrella software for it which I believe they will license for a fee to other landlords. Anyway you can read more about some of those issues and options in the following thread