Is it possible to open Hotspot while we are using wifi? I have tried but you can only use one at a time either WiFi or Hotspot but it'll be great if we can use hotspot while we are using WiFi.
No. Its not possible. 

Creating a WiFi Hotspot requires using the WiFi interface. And the interface, at the moment, supports using it for one thing at a time, either connecting to a Router with it, OR, creating a hotspot (router) for others to connect to.

As a side note, it would have even been nice to have your phone to connect two WiFis for faster browser. But that's also not possible either, at the moment.