I just released Universal Split Screen, which allows split screen on PC Minecraft with multiple keyboards and mice.
I've tested it on 1.13 to 1.14.4 and it should work on any future versions without updates.
You can download it here: https://universalsplitscreen.github.io/
There's also a video tutorial availible:
(On 1.14.4+, make sure to disable Raw input in Options -> Controls -> Mouse settings)