You seem very thoughtful and set in your calculus. It's probably no help, but for what it's worth, two kids is less than replacement value. Were every couple to have only two kids, the odds are some would die and you would have a shrinking, not growing, population. Having kids, at least in my experience, is a true blessing, and something that I think will bring me great joy for many decades. To each their own, but I wouldn't worry too much about environmental impacts or global carrying capacity.