Sorry but IMO, sibling jealousy and rivalry is only "normal" where the parents or whoever is raising the kids completely FAILS to promote love and respect amongst the siblings thus allowing them to sink to the low levels of fear, jealousy and rivalry. In a normal, healthy family, respect, friendship and love will be AUTOMATIC.
There would have been NO sibling rivalry or jealousy in my family (or any other family) if only our very inadequate parents had made even the slightest effort to encourage us kids to be KIND to each other! Sibling rivalry is ALWAYS the sad consequence of BAD PARENTING!