No. Vivo Y91 does not have the front camera flash but it does have the display flash. Which helps to capture good selfies in low light conditions.
No. Vivo Y91 does not have the hybrid sim slot. It has 2 dedicated slots for sim cards and a dedicated slot for the MicroSD card.
Yes, Vivo Y91 does have the fingerprint scanner. It also has the face unlock support.
Yes, Vivo Y91 does have the dual 4G support.