There's a weird dichotomy between siblings. On the one hand we want siblings to get along for obvious reasons. They have to live with each other for years anyway, and it makes for a peaceful household. On the other hand, siblings are never going to get along. By that I mean, yes there will be moments of love, but there will be just as many moments of pure hate and vitriol. It's a trade off that always balances out.
Still, even if siblings are going to fight, it's important to try to teach them peace. One extra large t-shirt from the gas station and some magic markers is a hell of a good price to pay for teaching your kids a lesson. Watch out though. There have been times where I've been so mad at my sister that I would have jumped off a cliff just to take her with me.