I was watching video on YouTube about a man who gave up one of his kidneys to his sister who was suffering from kidney disease. For him it was no small sacrifice, since he isn't in the best of health himself. Still, he had no hesitations over it and no regrets either. My friend has two sisters and once tried to explain to me how much he loves them both, even though one of them is a total brat who was always going out of her way to get him in trouble.
Richard Dawkins attempts to explain love between siblings in purely naturalistic terms: since siblings share many of the same genes and genes are the unit of evolution (according to Dawkins' "selfish gene" theory) it makes perfect sense for one sibling to endanger themselves or even sacrifice their life to save another, even though this degree of altruism might seem very anti-Darwinian on a superficial level.
That the WT has such a hold over people, strong enough to even turn siblings against each other, is sad but also amazing in a way. I'm an only child myself and if I did have siblings, I wouldn't want to abandon them; but I often wish I had the power to just turn off my emotions like that. Even when I was a JW, I wasn't able to do it. I couldn't shun my friend when he was DF'd and now that I am being shunned, I can't stop having feelings for those who are shunning me. Like most people, I am perfectly capable of shutting down emotionally in a crises so I can do whatever needs to be done; but when the crises is over all those feelings return and I am forced to deal with them. I sometimes wonder if this ability really has anything to do with being a JW. Maybe permanently shutting down one's emotions is just a natural capacity that some people have, but which JWs simply have more opportunities to exercise. As terrible as it is, I can't help but admire it. It's like they are just born with this perfect, Buddhist detachment which actual Buddhists struggle to develop over lifetimes.