I think Alice-senpai and the student council president are brothers (like twins) or something, but they are related for sure because Rina asked if she can say the president's name.
Also, how can Tachibana be so sure that he's the one Tendou likes? How can he be sure that her feelings haven't changed? It's just that, his interference with Tendou's confession is kinda... too much. Like he's so sure of her feelings for him. What made him so sure though?