Multistore - all items in main store

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Hi. We are trying to configure our store, but after spending a day I'm out of ideas. 

In short. We have a shop with clothes. 

- "Main" store

- Few smaller "substores" for graphics designers/artist

We want to provide  external access and create (independent - in terms of sold items etc) substores for them, but we want to promote their content in our ("main") store too. So:

- "Main" store should display our items + all other from "substores" too and simultaneously their "substores" should only display their own content.

Is it possible to do something like this? Thanks for any help in advance.

Edited March 6, 2018 by Link (see edit history)