I like give Tony a brother, that could lead to some interesting stories, but i believe every heroes origin should be simple and easy to explain. This just muddies the water and makes everything convoluted
I would disagree with that. His superhero origin is still the same - kidnapped by terrorists and forced to build the Iron Man suit to save his own life, became superhero, etc. This just changes his birth origin, which was never important to his superhero origin (other than being the son of a billionaire, which he still is, adopted or not).
They should say Howard Stark lied to his wife for Tony adoption but he was actually Howard son through another woman because he was not sure his wife could conceive this story should be better and would explain why Tony looks so much like him and up to the end Mrs Stark thought Tony was adopted because for me this new origin remove the magic of the character
I think it will be something like this. I'm still betting on Tony being Howard's bio son in some way (but it doesn't change any of the character "magic" for me, because him being Howard's son was never a big deal for me).
The only thing that changed is that Tony's family just got bigger (which he and Arno both seemed pretty happy about). Poor Arno, he's probably been sitting alone in that hospice for about 15-20 years (or however long its been since Maria and Howard died).