No. Redmi Y2 can support only one 4G sim card at a time. Another sim card will work either on 2G or 3G network as per your preference.
Yes, Redmi Y2 does have a dedicated MicroSD card slot. You can use 2 sim cards and a memory card at the same time.
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 front camera flash.
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.