Yes, Redmi 6A does have 3 slots - 2 for sim cards and 1 for the MicroSD card.
No. Redmi 6A does not come with the earphone in the box. You have to buy it separately.
Yes, Redmi 6A does have the face unlock.
Yes. Redmi 6A is definitely better than Redmi 5A in many ways.
Redmi 6A released in 2018 while Redmi 5A released in 2017.
Redmi 6A has 5.45 inch 18:9 display while Redmi 5A had 16:9 display. Both phones have 295 & 294 PPI resolution respectively.
Both phones have similar RAM & internal storage but Redmi 5A used to have a hybrid sim slot while Redmi 6A has a dedicated MicroSD card slot.
Both phones have the same camera features. Both phones have a similar 13MP rear camera and 5MP front camera. But Redmi 6A has face unlock which is not available in Redmi 5A.
Redmi 6A is based on Android 8.1 while 5A is based on Android 7.1.
One more important difference is Redmi 6A is a dual 4G phone while in 5A you can use only one sim card on the 4G network.
We also suggest you check the video below which gives a complete comparison idea.
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.