According to HK fans' news, SUJU have gone to HK to do some photo-shooting.
So all 13 of them will be present.
Till now, Heechul, Sungmin and Kangin arrived HK at yesterday noon, while M (Geng, Hae, Kyu, Ryeo and Won) arrived at night. That explains the photos of M in Incheon Airport. They are staying at a hotel in Tsim Sha Tsui and they are probably leaving HK on 30th.
However, because this visiting and photoshooting is not officially announced, so some news are not confirmed and maybe fake.
8.27 Night - Heechul, Sungmin and Kangin went to Lan Kwai Fong to shoot, while M went to Victoria Habour.
8.28 12:45pm - M are at Golden Coast. Yesung, Teuk, Hyuk and Shindong arrived HK and are heading to there.
Source: Soompi Thread (#1), Soompi Thread (#2)
Don't really follow them much, but dang this shot needs a professional photobook version ASAP.