Yes, Vivo Y81i does have the OTG support.
Yes, Vivo Y81i does support GPS.
Vivo Y81i has 2GB RAM of LPDDR3 type.
Vivo Y81i comes with 5V / 1A charger. It does not support the fast charging.
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.