No. Oppo A5s does not have the dual front camera but it has the dual rear camera set up.
Yes, Oppo A5s does have the support for the face unlock. Besides, it also has a fingerprint sensor.
Yes, Oppo A5s has a dual rear camera set up. The primary rear camera has a resolution of 13MP while the secondary rear camera is of 2MP resolution.
Yes, Oppo A5s does have the OTG support.