Is it possible to run an app twice side by side on the MIUI? It is said that with MIUI, it is possible to run the same app twice as if they are on two different phones. (example: WeChat or Line running with a work account and one running with a personal account).

Is it possible to run the same app twice, and side by side on an Xiaomi Redmi 4X with MIUI 8?  Or is it only possible to show them one at a time? 

If it is only possible to show one at a time, you can't really play some games such as Pokemon Go and do the Raid Battle at the same time using both accounts (since you have to switch screen to one at a time and therefore not play at the same time).

And if it is possible side by side, can it be vertically or horizontally split on the screen, but won't the 2 apps be really small and make it not practical to play at the same time?

Could some screenshot / YouTube video be posted if you are possible to make it happen?
You can't play the same game simultaneously, while gaming the active window only will be active in split-screen mode (see the example below), but you can play while you're watching Youtube, because gaming isn't like watching or listening. 


  
  Your device has a 1.4GHz octa-core and 2GB, it's not a high end device where you can run resource consuming apps twice, your chances of getting things up and running are low.
  The app cloning feature is good for WeChat,Line and other chat apps but not for gaming apps where your 5" device is not enough to run two instances in a split screen.
  The following solution is almost for every Android Device with high end specs:
  


1. Force activities to be resizable

To force apps that doesn't support split screen feature, you have to enable this option from Developer Settings:


Goto Developer Options.
Scroll down and until "Force activities to be resizable" and activate it.
Restart your device.


Now, you can use split-screen with any app, even if it doesn't support split screen feature.

2. Install Parallel Space &amp; Parallel Space - 64Bit Support


  Note: Parallel Space has access to many dangerous permissions



Launch Parallel Space and choose the apps you want to clone.
Launch the cloned instance of your app.
Tap &amp; maintain on recents button to split the screen.
Launch the same app from your recents or from your home screen.


3. Example: Two instances of Clash Royale

In the picture below I'm Playing Clash Royale and Clash of Clans (by default they don't support split-screen feature) in split-screen but not simultaneously.