Well I don't know if Samir is MC's bro...Samir used MC for his own selfish benefit. Remember MC wasn't aware of a hidden deal that involved Samir's use of one of the widower's houses and bar. And because of that deal, I believe MC was forced to give up more than he wanted... 10%-20% of the family's very valuable modeling agency (which really wasn't his to give any part of), if MC wanted the widower's support for his path to be emperor. (But I'm not sure if killing the guy was the best choice...now) Also, I used the 0x52_URM tool to show me what points is are behind the game choices... (During my first playthrough I picked 20%, and missed out that the 10% choice worked as well....I was only picking choices that gave points.)
And then when Samir gave one of his girl friends an ultimatum of one week, to get MC's childhood friend on board with MC's way of life...she ended up drugging her, because she was pressured by Samir. So it's obvious Samir is known to cause others trouble, that I believe might end up biting MC in the ass later...if he isn't careful.