99% of the things that siblings fight over tend to be hilariously dumb.
And it doesn't change too much when they grow up.
After my paternal grandmother died, all her 6 children, sticking together pretty well thus far, got into a big war about the inheritance. Which wasn't even anything worth it, just some scraps and bits of scattered farming plots and forest. It's all too bad, the atmosphere between them could have been really great earlier, but this situation has soured everything for over a decade and only recently there were some signs of improvement. At least not much of the conflict has trickled down to their children it turn, that is, my generation...
The fight was particularly heated about one sandy patch of ground on which nothing wanted to grow. But they were told that a highway will be built there, so the person owning the place would get a juicy compensation. Plot twist: the highway is really under construction currently, but on the opposite side of the village!
So the one who won the fight remained with a useless ground piece that can be even hard to sell.
Edit: I didn't mean that they were physically fighting, but there was a lot of quarreling, angry phone calls, things like that, also so me administrative and legal trickery.
What kind of reverse psychology nonsense is this?!
But I can have it like this too! When denied something, I can get "offended" at the thing in question and start kind of hating it instead.