Yes, Redmi Y2 does have the portrait mode for the rear camera. The front camera does not have the portrait mode.
Yes, Redmi Y2 does have the dual app support.
Yes, Redmi Y2 does have the front camera flash.
Yes, Redmi Y2 does have a dedicated MicroSD card slot. You can use 2 sim cards and a memory card at the same time.
The Xiaomi Redmi Y2 is a slightly better attempt at a selfie-focused smartphone than the model it replaces. It has proven hardware that is capable of delivering a smooth user experience, plus MIUI 9.5 which has a lot of added features.