Yeah, Reina-wise, I'd think that the rest of MM probably think of her just like Nonaka or Haachin, as someone who passed the audition fresh rather than a KSS, but ever since they first started taking in KSS for new Gens there has been that kind of thing, so I don't think it will be awkward at all to be honest. They've been very careful to introduce Reina before Kaede, knowing that Reina wouldn't be able to follow after the Kaede reaction, and Kaede has been very excited/accepting towards Reina as well. I think the fact that Reina was not super young will make them seem like a pair despite the experience difference. The reaction when she saw that Reina was the other 13th Gen was one of happiness and relief so I think that she was really worried about having a eleven year old as her gen mate.
Also watching all the reaction and announcement stuff, I didn't realize how much some of the MM girls cared for/were friends with Kaede. Masaki in particular reacted so strongly to everything and was so excited to have her announced at the concert.
This is going to be a star-power of a generation. I don't see them being shafted for their first single like 12th did (I still like to think of The Vision as their true debut song). Reina is just too adorable not to focus on and Kaede is too popular.