Have you tried:
So what you will need to do is follow a few steps to enable splitscreen.
1.) Go to your project settings > Maps and Modes > Use Splitscreen
This only enables the use of splitscreen and does not draw it on your screen when you PIE or play in standalone
2.) You will need to go to your level blueprint and add a " Create Player " node. You will need to uncheck context sensitivity. Then add an “Event BeginPlay” node and plug that into the “Create Player” node.
3.) Compile and play.
You can change the vertical or horizontal orientation back in the project settings where you enabled the splitscreen.
Solution from this post: How do I setup to multiple cameras to do something like split-screen? - #5 by anonymous_user_0345a438