Approach that can be used if only 2 instance of a particular class is needed.

[Jyoti Aggarwal]

In singleton pattern we have to use just one instance of a particular class. What is the approach that can be used if at any particulay moment just 2 or 3 instance of a particular class need to exist.

[Jan Cumps]

You adapt the Singleton class to manage and restrict the number of instances.
The implementation that is used by the Gang of Four checks if one instance exists. If yes, it returns that instance, if no, it creates a new one and returns that.

In your Singleton implementation, you will need to do the bookkeeping to count how many instances are existing, and create a new one if needed/allowed.
But then, which one of the 2 instances are you going to return? The first one? The second one? You will have to define the logic for that.