You'll notice I updated the wording above. "Step child" in this case was totally the wrong word for Steve. The worst thing was that when I tried adding the adoptive parents, the program deleted the biological ones--and that would incorrectly display his genealogy. So, I went back to listing the biological ones.
But Steve's own thought that his adoptive parents were his "real" parents is probably typical of a lot of adoptive people. (It always struck me as "wrong" how he was on a nearby branch in the family tree, but not "with" my wife and her brother. Do you know what I mean?)