No animal deserves to be treated like that, fish or otherwise. In my opinion, buying them a setup yourself treats a symptom, but not the whole issue. Could you offer (possibly with the knowledge of your father) to teach your siblings proper care, help them pick out a good habitat, etc., with the other option that the fish are rehomed (to you or some other person who knows how to properly care for fish, not back to Wal-Mart)? It doesn't seem fair to me that you got in trouble if your fish weren't taken care of while your siblings are getting away with treating their fish cruelly.
It's funnier in Enochian.