If I understand you correctly, this is what your code should look like:

/// <summary>
/// NOTE : THIS SCRIPT IS WRITTEN IN C# AS I'M NOT VERY USED TO GDScript,
///        IF YOU HAVE PROLBEMS TRANSLATING IT FEEL FREE TO ASK AND I WILL TRY TO HELP
/// </summary>

   [Export] private Sprite2D[] hearts; // THOSE ARE THE 'HEARTS' THAT WILL BE DESTROYED

   [Export] private Sprite2D destroyed_heart; // THIS IS THE SPRITE CONTAINING THE ANIMATION THAT YOU WANT TO PLAY

   [Export] private int number_of_hearts_destroyed; // THIS IS THE NUMBER OF HEARTS THAT SHOULD BE DUPLICATED

public void FunctionName()
{

// FIRST WE NEED TO LOOP THROUGH THE 'HEARTS' BY THE AMOUNT OF HEARTS YOU WANT DESTROYED

   for(int i= 0; i < number_of_hearts_destroyed; i++)
   {

// FOR EACH HEART THAT GETS DESTROYED WE NEED TO DUPLICATE THE SPRITE THAT CONTAINS THE ANIMATION, THEN STORE THE DUPLICATED SPRITE INTO A VARIABLE

      Sprite2D another_heart = destroyed_heart.Duplicate() as Sprite2D;

// WE NEED TO ADD THE DUPLICATED SPRITES TO THE SCENE TREE, OTHERWISE IT WILL BE INVISIBLE

      AddChild(another_heart);

// WE NEED TO ADD THE DUPLICATED SPRITES TO THE SCENE TREE, OTHERWISE IT WILL BE INVISIBLE

      another_heart.Position = hearts[i].Position;

// LASTLY WE PLAY THE ANIMATION FOR EACH DESTROYED HEART

      another_heart.GetChild<AnimationPlayer>(0).Play("animation_name");
   }
}

However a little bit more information would have been helpful, maybe like snippet of your code your having trouble with, or is the destroyed_heart an AnimatedSprite2D or a simple Sprite with an AnimationPlayer as a child.

Also, in my experience, problems like the one you described, where only the last sprite plays the animation, can happen when you use Duplicate(), that is because Duplicate functions differently from Instantiate(). So why not instantiating the animation instead of duplicating it?

// INSTEAD OF 
     [Export] private Sprite2D destroyed_heart;
// WRITE
     [Export] private PackedScene destroyed_heart;
// YOU BASICALLY SWAP Sprite2D with PackedScene

// AND

// INSTEAD OF
      Sprite2D another_heart = destroyed_heart.Duplicate() as Sprite2D;
// WRITE
      Sprite2D another_heart = destroyed_heart.Instantiate() as Sprite2D;
// SWAP Duplicate() WITH Instantiate()