The fork of forklift B is under forklift A. If forklift A tries to lift formlift B, it cannot, because the fork of forklift B would get lifted up as well, but is stuck underneath forklift A.

Therefore, you can achieve the precisely same result by removing forklift B from the equation and turning the fork of forklift A around so that it is pointing backwards and underneath forklift A itself. Now, with your own form underneath yourself, lift the fork up.

It does not matter who the fork stuck underneath you officially belongs to, if what you are trying to do is to lift said fork up.