As father to three children, my experience is that you only think two is exponentially more complex than one. At least with two, they don't always outnumber you!
Also, thanks to combinatorics, the number of sibling fights that can happen increases superlinearly:
With a simplifying assumption of only pairs of siblings getting into fights, its C(n,2) which is 0,1,3,6,10,15 for 1-6 kids. I have a friend with 6 kids and can confirm that there are roughly 15x as many fights between the siblings as friends with 2 kids. Age differences do matter though (if your kids are much more than about 10 years apart, they tend to clash a bit less because they are less in competition with each other).