Re-reading this makes me realize that Ritsu was already talking about her brother in here. They must be pretty close (or at least have an ok relationship) for her to talk about him so much on the show.
I'm 99% sure that Tsumugi won't be one of the 5 girl being debuted, but I sure hope that she can grow independent, free from her sister after this competition, for both of their sake.
thanks for the chapter!