Phew. You sometimes don't think about how these things can have such a big impact.
I have been married now for 7 years and have become a son richer. Before we got married, my wife was a single mother with her son not knowing his biological father and paternal family at all. He only met his father when he was 18 on his request. My wife often tells me how she dreaded a lot of the same things you have highlighted above when it came to her son. Like the family tree, fathers day, etc.
So I think what you are proposing here is relevant for more than just adoption and should definitely be applied in schools.
Thank you for a great post!