Due to lack of support by DELL and its DDM software (Dell Display Manager) on macOS, we solved it with the giant help of a group of talented programmers and curious foxes around the world.

My Setup Studio: Macbook Pro 15´+ Mac Desktop (Hackintosh) both connected to a pair of DELL P2417H monitor. The first programing approach was made by Joey Korkames for controlling brightness and other functions from macOS terminal. And the continuation of implementing those lines to control the input switching, by Patrick Rynhart @prynhart from New Zealand. With him, solving that tricky part, made an Automation Script for each machine, invoking the proper Terminal code lines and fired it with a custom key with the app Keyboard Maestro.

Go here for video.