No. Redmi 6A does not have the front camera flash.
No. Redmi 6A does not have IR remote sensor. You cannot control your TV or AC with it.
No. Redmi 6A does not have the removable battery. It has a nonremovable battery.
Yes, Redmi 6A does have 3 slots - 2 for sim cards and 1 for the MicroSD card.
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.