This thread is really just ridiculous. If you are unwilling to do anything proactive about the situation (ie. rehoming the fish and then taking a sledgehammer to the tank so they can't get any more), I would just ignore it completely and your friends will grow tired of spending their money and having nothing to show for it soon enough.
IMO, by you "helping" keep the fish alive, by doing some water changes etc., while they just continue (and I am sure will continue for a while) to get new fish and ignore the tank, you are just prolonging the inevitable. Those fish will all die, and your friends will eventually get bored and stop buying more. The longer the fish stay just barely alive, the more fish they will continue to get, the more fish will eventually suffer and die in this tank-o-death. So I would wash your hands of the whole thing, and then hopefully get some new friends that have a modicum of intelligence and maturity.