This article on sibling abuse raises some interesting points on why it happens and signs to look out for.
It does seem to be focused mainly on sibling sexual abuse rather than physical or emotional abuse. All forms of sibling abuse are hard to get statistics for as in all the studies I’ve researched the sibling figures are included in “other family” general categories.
This quote from the article on impact for me is key for people to understand:
WHAT ARE THE LONG-TERM EFFECTS OF SIBLING ABUSE?
Time does not necessarily heal. Adult victims of childhood sibling abuse generally have lower self-esteem and are overly sensitive and insecure. They have trouble with relationships and repeat the victim role in their other relationships. They can have sexual functioning problems. There is continued self-blame at the same time that anger at their perpetrator is played out with others.