This is the parent:
Killer Instinct 2 (v1.4)

These are it's clones:
Killer Instinct 2 (v1.0)
Killer Instinct 2 (v1.1)
Killer Instinct 2 (v1.3)
Killer Instinct 2 (v1.4k, upgrade kit)

So, you need Killer Instinct 2 (v1.4) and the CHD file.

If you want to play the clones (might be some difference in game play) then you need to also download that clone and the CHD file (they all use the same CHD file)

To play a clone, you also need to have the parent.
But to play the parent you don't need the clones.

Is this starting to make sense to you now?