That's what I thought was going to happen too. We're still 2 girls left right? Are they the two girls whose faces are hidden here? Maybe they won't even get introduced
Yup, we're at 3/5 girls from the original idol group. Ayumi was introduced in chap 15 and Souko in chap 27, so I guess we should have a new encounter soon.
Seems that the only 2 images where we have clues about the remaining members are the one I sent above and these panels from Souko's flashback in chapter 32:

So it would seem logical that in the first image, from left to right, we have: unknown (hidden), Ayumi, Sumire, Sayuri (not introduced), Souko (hidden).
Btw, Sumire said in chapter 1 that of the two remaining girls, one had returned to her family's home in the countryside and the other was still doing some idol work (which had led me to believe that Sayuri might actually be Unico).