Yes, Vivo Y81i does have the OTG support.
No. Vivo Y81i does not have the front camera flash.
No. Vivo Y81i does not have the removable battery.
No. Vivo Y81i has 2 dedicated slots for sim cards and a dedicated MicroSD card slot. You can use 2 sim cards and a memory card at the same time.
Yes, Vivo Y81i does have the virtual gyroscope sensor.