I feel so bad for Colette. Granted, the date came out because everyone wanted Will to join them. Colette always did have Will all to herself for the most part, but never was able to capitalize on it from what we know. Given all the clues describing Rosti and Will's friendship and how they have been so close since knowing each other. It makes pretty obvious who Rosti is.
Lihanna giving off heavy Ais vibes of being the top in her class, but an airhead. For Lihanna there is one interesting thing where she ambitions to seek to become a Magia Vander and the fact she called all 4 of the mages present are leftovers. This perhaps gives an indication sure advancing the tower is one thing, but becoming a Magia Vander will be quite the task in itself. At the very least, she is very diligent, and her motivations are clear.
Similar to Lihanna Wignall brings a different dynamic. He doesn't mention what he thinks of Will, but he has some valid points. Lihanna tops him in the school and at the very least he has to respect her position to recruit Will even if she doesn't really explain why she wants him in the group. Also, Sion & Julius looking down on Will humors him since Will bested both of them. Like Lihanna he seems very logical, though he does seem to have more of a personality than her. Interesting group and obviously, Colette had to include herself.
Spoilers? Or are we talking about different shows?