I don't think they're twins, I think the brother is keeping watch of him since he is a little crazy. His face in certain panels reflects how he's trying to be perfect and crafting a perfect relationship but has deep thoughts of possessiveness among other feelings. His brother showed up at the school, and all of a sudden the ML asked MC "Why do you like me?" It looks like either the MLs brother either knows about his brothers tendency to obsess, or his truly wealthy lifestyle- OR he's from one of those wealthy families that in their constant butting in, vets whoever the ML speaks to.
Which is probably why we see the ML take the MC to a fancy restaurant and ask about his goals. ML wants to probably prove his brother wrong that MC only likes him because he's being fake and acting humble/ acting like he doesn't have the means. Though I feel MC already knows he's rich.
Did the MC figure out that the ML was the same guy in the wheelchair from the other reality before he died yet?
He did
Thank you!! The wait for the reveal was killing me so I decided to let it marinate, I'm so happy he knows!