No. Redmi Y2 can support only one sim card on 4G network at a time. Another sim card will be either on 2G or 3G network.
Yes, You can have 2 different WhatsApp account on Redmi Y2.
Yes, Redmi Y2 does have the fingerprint scanner & face unlock, too.
No. You can not record slow-motion video with Redmi Y2.
Yes, Redmi Y2 does have the support for Miracast.
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.