As an only child with absolutely no model to work with, I feel like things are working out pretty well between Paige and Isaac and I don't need some selfie-helpie, touchy-feely book to tell me otherwise. I prefer a "natural," Darwinism-type approach to parenting siblings, where just as in caveman days, the children compete for resources and aggressively attack each other to get them. I call this "Paleo Parenting."
Under this model, the kids engage in physical and psychological warfare and may the most evolutionarily fit child win! Intervention is called for only when it appears that life and/or limb and/or an eyeball is truly at risk.
The below photo is a good illustration of Paleo Parenting at work. Here I have dumped this year's Halloween bounty onto the giant foam puzzle map in the middle of the living room floor. It's up to the siblings to scramble and strategize for the most "nutritious" items. Kind of like The Hunger Games. And they better hope they each manage to score some Snickers, because the one who only gets Nerds and Sour Patch Kids will not be passing on their genes. So "Siblings Without Rivalry" can go suck a dick. Long live Paleo Parenting!