Yes, Vivo Y81i does have the virtual gyroscope sensor.
Vivo Y81i has 2GB RAM of LPDDR3 type.
Yes, Vivo Y81i does support the face unlock.
Yes, Vivo Y81i does support GPS.
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.