1, none of my kids or grandkids have ever encountered this issue. But that isn’t relevant to this discussion.
But even you admit parental abuse is more pervasive than sibling abuse. What are you doing to keep parents away from children unsupervised? Since parental abuse is both worse and more frequent than sibling abuse, something virtually everyone agrees about, it’s more important to keep parents away from their children unsupervised than keeping siblings away from each other unsupervised.