Multiple sites?

I have a few relatives and a few clients interested in smartthings.
Is it possible to set each up on its system but that I can have access to all, without allowing access between clients?

The SmartThings App is pretty limited in flexibility with respect to Account / Location sharing. It is very hard to set limitations; but it’s with setting up 2 Hubs (or a Hub-less Location in the IDE?) and experimenting. There are some existing Topics on sharing you should search for.

For “view and control” (but not add/remove Things and configure SmartApps) ActionTiles has unlimited granular sharing at the dashboard Panels level and a Location can be connected to specific multiple ActionTiles Accounts if desired.