One GameInstance: Multi Windows x Multi Views (Multi Monitors Support). Just use the Blueprints.
Demo Video: https://youtu.be/SfOjjzGyvCY
Multi Windows: Create multi windows for your one game instance.
Multi Views: After creating multi windows for one game instance, you can create multi views for any one window.
Multi Monitors Support: Can move any created window to any monitor and resize the window or make it full-screen.
Number of C++ Classes: 12
Network Replicated: (No)
Supported Development Platforms: Windows; Mac; Linux.
Supported Target Build Platforms: Win64; Win32; Mac; Linux.
Example Projects And Documents: https://gitlab.com/UE4MarketplaceSubmission_Public/multiwindows4ue4_public