Multisite with some shared content and some different content I need to create 7 magazine sites with different themes but some content should be shared (like some common pages, some pictures etc). 

There should be a common control panel for all websitea so that my customer can upload data on all websites from the same panel. The same content is required because the customer will upload articles on one and it should publish on all site.

I have already setup two demo site with different database on one hosting place and single Drupal installation.
You don't really want a multi-site at all by the sounds of it. You're looking for Domain Access


  The Domain Access project is a suite of modules that provide tools for
  running a group of affiliated sites from one Drupal installation and a
  single shared database. The module allows you to share users, content,
  and configurations across a group of sites such as:
  
  
  example.com
  one.example.com
  two.example.com
  my.example.com
  thisexample.com &lt;-- can use any domain string
  example.com:3000 &lt;-- treats non-standard ports as unique
  


In fact, the ORIGINAL use case for Domain Access was for magazine sites (from the documentation), so it should fit your needs perfectly!