With that said, after I presented my questions in layman's terms, this plethora of walking knowledge confirmed what Mitch and I were believing for each of the girls' left kidney.
Both girls' kidneys are functioning perfectly. They both are draining completely. The scan shows that Norah's left kidney appears to be a tad bigger than her right, and appears to be draining slower--but it's not causing any problems. ( I mean, my love for dessert appears to be a tad bigger than most and that's not causing any problems, at least not yet.) He'd like to see her back in 6 months for a little Ultrasound and Hazel in 12 months. It looks to him that they are growing out of this. And, he "highly" doubts that the girls will ever need any kind of surgery for this.
(a sigh of relief)
Now, on to buying a couple of those SuperYard XTs.