Yes, Redmi 6A is a dual-4G phone. You can use 2 Jio 4G sim card in Redmi 6A.
No. Redmi 6A does not have the front camera flash.
Yes, Redmi 6A does have the GPS support.
The Redmi 6A is a fairly good update to the Redmi 5A, which itself was barely any different compared to the Redmi 4A. You now get a tall screen, better processor, and improved polish overall.