If I’m receiving multiple messages instance of same format then how many orchestration instances will be created and how can I check what are the instances it has created in Admin console?
The default behaviour is too get as many Orchestrations as you have message instances. If you don't want this you need to follow other patterns such as Singleton Orchestration, Convoy Orchestrations or Throttling Orchestration pattern.
You can see the current Orchestrations under Running Instances and those that have finished under Tracked Instances.