The fact that the brother was mentioned twice and didn't let us see his face, it's gotta be him. I really hope for this type of f-buddy troupe for the ML to fell in love first.
But wasn't the older brother 29 years old? It said on his profile when that female student looked him up. MC is 26, unless MC got into school young/early or the older brother was late into school, otherwise they can't be classmates.
I love whatever is wrong with both of them (positive)