Probably Keine and Mokou, but I'm not sure...

Well, Mokou is mentioned by name so we know she's there, but I wouldn't tag the other until we know for certain.

Judging by the hairstyle (particularly the bangs) and taking into account those whom Mokou might visit a hot springs with, it's probably a safe assumption that it's Keine. But yeah, best to be sure before tagging someone.

...It's Keine. Looket the hair; darker vertical stripes near the front and side of her face. that's no shading, gents.