Although it isn't ideal, it is natural for siblings to fight.
My father has the story of his older brother jamming a lawn jart through his palm into the grass. They both ended up going to Nam. My uncle was an airline pilot and has now been high up in the FAA for over 35 years and my father still hasn't forgiven him since there has been no apology. The families still visit, but it is not forgotten.
My older brother stole many things from me. We got into quite a few fights. I was a skinny wimp but at one point I slammed his head into a coffee table which caused him to have 15 stitches in his head. I visited him in the pokey this last Sunday and wish that he was still around to kick my ass.
This crap should be left alone unless there is serious sexual or life threatening injuries occurring. Otherwise sibling fighting should be handled by the parents.
"Give us a kiss, big tits."