No. Oppo A3s is not a waterproof mobile.
Yes, Oppo A3s does have the face unlock.
Yes, Oppo A3s does have the dual rear camera. It is 13MP + 2MP dual camera at the rear.
No. Oppo A3s does not have the Corning Gorilla Glass protection. Ideally, to protect the display, you should use tempered glass over it.