If we assume that the human spirit is the product of the mother and father, then you may have something. I have already considered much of what you have said and my first response is frankly that I do not pretend to know or to be able to explain how humans and angels could mate. My understanding of this passage is based off of exegesis and not science, much less genetics. Therefore I believe that we are made in the image of both God and angels. You said that angels temporarily take on human form.
Some angles have wings.
But this does not mean that they all do. Most importantly, our understanding of what angels can and cannot do is so limited that I do not believe any of us are in a position to make dogmatic statments about these beings. The argument about God's order for the animal kingdom does not apply. As you yourself mentioned, there was no intercourse involved with Mary. I do believe that there was intercourse in Genesis 6.