So I was right, the new characters are Kurusu Kanata (seiyuu: Kugimiya Rie) and Makishima Kaori (seiyuu: Houko Kuwashima)
Both are members of Pretty Garden, Saori's ex-circle.
Kanata is Kanako's older sister. The round glasses Saori wore was originally her. She is a mangaka and use pen name. She will appear on Kanako and Saori route.
Kaori is Saori's older sister and the founder of Pretty Garden circle. Will appear on Saori route.
Those are from third weekly article. We also get to see the preview of Live2D sprite of Ruri on Shironeko outfit (page 2)
http://news.dengeki.com/elem/000/000/450/450079/