You didn't get the idea of a multistore at all.
Multistore means that you have only one installation that handles all your stores. These stores can have different domains associated, you just need them to point to the same IP address you thirtybees is running on. When visitors visits any one of these stores, thirtybees will determine the correct shop context from the url, and will serve content from that shop only.
Of course, you can decide if your mutli-stores will share products, customers, orders, etc. You can set it as you wish.
The main benefit of multistore is that you can manage everything from one back office