In my post about family, I completely forgot (and so did Moffat apparently) that Danny came from some kind of children’s home, and may not have a family in the traditional sense. It is of course possible that he was adopted and acquired a family; he is also never clearly stated to be alone.
However, rather than undermining what I said yesterday, this supports it. It’s an enormous gap in our knowledge and understanding of Danny. Moffat likes to say that of course such and such happened, we just didn’t see it. Well, I want to see it, dammit. If it happened, if it’s part of the story, put it on screen.