Yes, Redmi 6A is a dual sim mobile phone. It also has a dedicated MicroSD card slot.
No. Redmi 6A does not have Dolby Digital sound support.
Yes, Redmi 6A does have the GPS support.
No. Redmi 6A does not have the NFC 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.