The twin analogy is extremely weak. In this case the twin’s unfortunate circumstance is no fault of your own. You didn’t actively make any decision to put them in their situation of urgently needing you to survive.

You need to alter your analogy such that you made some conscious decision that you knew could injure your twin brother, rendering him in need of one of your kidneys to live. At that point you have to show why it’s moral for you to withhold the organ donation.