The theory that the N7 is a parent character instead of a sibling character is not a bad one and the dynamic has the potential to be interesting but I am still holding out hope for my Bro-Bro = N7 theory.
While it depends on how it may be executed, I have the potential to be happy with either theory turning out to be true so let's keep on hoping 
Bro-Bro is basically what I've been calling the theorised N7 sibling character. What about Pa7 or Papa-7 for the parent character theory? Papa-7 = N7 theory? 
I recall one sibling definitely looked older in that family photo, so the older sibling could definitely be the N7. (I need to look it up, again.)
I think it's humorous how obsessed people have become with the "N7 antagonist" idea. When I suggested it, I didn't really have a lot of evidence. My reasoning was simply that they said he was "not our PC", but "is plot critical". People have latched onto that passing thought/theory and refused to put it aside, for now.
Hopefully the first novel releases on schedule, and isn't delayed to match the game delay. The novel should answer a number of questions.